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General Network Working Group Internet-Draft The North American Numbering Plan (NANP) is projected to exhaust available telephone numbering resources within the coming decades under current allocation and utilization trends. Existing mitigation strategies, including area code overlays and number pooling, extend the usable life of the NANP but introduce increasing operational complexity and user confusion. This document proposes a long-term, uniform expansion of NANP telephone numbers from 10 to 11 digits through extension of the area code or Numbering Plan Area (NPA) from 3 to 4 digits. The proposal emphasizes backward compatibility, fixed-length numbering, and a multi-phase transition strategy designed to minimize disruption. This document is intended to stimulate discussion and does not represent the position of any standards body or regulatory authority. Status information for this document may be found at . Source for this draft and an issue tracker can be found at .

Executive Summary The North American Numbering Plan (NANP), which governs the 10-digit telephone numbers used across the US, Canada, and partner nations, faces eventual exhaustion of its numbering capacity. Current stopgap measures — area code overlays and number pooling — extend the system's lifespan but compound routing complexity and degrade user experience.

The Core Proposal This document proposes expanding NANP telephone numbers from 10 to 11 digits by enlarging the area code field from three digits to four digits: Current: NPA-NXX-XXXX Proposed: NPAX-NXX-XXXX The central design choice is to preserve fixed-length, fixed-position parsing. During the initial transition, the added fourth area-code digit would be uniformly limited to either 0 or 1, because current NANP NXX prefixes begin with digits 2 through 9. That lets switching systems distinguish old 10-digit numbers from new 11-digit numbers by examining the fourth digit, avoiding variable-length dialing, timing ambiguity, or major changes to downstream routing logic. Rather than altering the subscriber number or prefix (NXX), the proposal extends only the area code field. Since the NXX of a subscriber telephone number cannot start with 0 or 1, that is used to modify the area code (NPA), by appending it with either a 0 or a 1. A number like 213-555-1234 would become 2130-555-1234 or 2131-555-1234. The fourth digit is initially restricted to 0 or 1, which allows switching systems to distinguish new 11-digit numbers from legacy 10-digit numbers by a simple positional check — no timing-based or variable-length parsing required. In a later phase, digits 2–9 would be unlocked, expanding total addressable area codes roughly tenfold (from ~700 usable NPAs today to over 7,000 NPAXs).

Why This Approach The proposal explicitly rejects several alternatives — expanding the subscriber prefix or line number, variable-length numbering, and relying solely on reserved NPA ranges — on grounds that each would impose greater infrastructure cost, database bloat, or user disruption than the NPA extension approach. The NXX and XXXX fields are left entirely unchanged, which preserves existing routing tables and local number portability (LNP) database schemas.

Transition Strategy The proposal outlines a five-phase migration: Phase 0 — Silent infrastructure readiness (networks updated, no public announcement) Phase 1 — Dual-format acceptance (both 10- and 11-digit numbers routed simultaneously) Phase 2 — Public notification, first via announcement, then via intercept warnings on legacy 10-digit calls (calls still complete) Phase 3 — Mandatory 11-digit dialing (legacy format calls rejected with a SIT-tone intercept) Phase 4 — Full expansion (fourth digit opened to 0–9, unlocking the complete numbering pool)

Alternatives Considered and Rejected The document evaluates and dismisses further number pooling subdivision, overlay-only strategies, variable-length numbering, expansion of the NXX to four digits, and expansion of the line number to five digits. Each alternative either provides insufficient long-term relief or introduces greater disruption to routing infrastructure, portability databases, and switch hardware than the NPAX approach.

Key Risks Backward compatibility is the primary concern. Hard-coded 10-digit fields in software, embedded devices (elevator phones, alarm systems, card terminals), 911/E-911/PSAP infrastructure, and legacy PBX systems will all require remediation. Security systems such as STIR/SHAKEN call authentication must be updated to handle both formats during transition. The draft stresses early planning to avoid a time-pressured implementation.

Scope The proposed format remains within the ITU-T E.164 15-digit maximum and requires no change to the +1 country code. This document is an informational discussion draft and does not represent the position of any standards body or regulatory authority.

Introduction The NANP currently utilizes a fixed-length 10-digit numbering format (NPA-NXX-XXXX). Growth in telecommunications services, device proliferation, and number portability has steadily increased demand for numbering resources. Mitigation strategies such as overlays and thousands-block number pooling have delayed exhaustion but introduce increasing complexity in routing, administration, and user experience. This document explores a uniform expansion of NANP numbers to 11 digits as a long-term solution. This proposal preserves fixed-position digit parsing, avoiding variable-length interpretation and timing-based ambiguity. This property is a primary design objective, as it minimizes required changes to existing switching and routing infrastructure.

Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Definitions

CP:

is Cellular Provider, the service provider for a caller using cellular telephony.

IXC:

Interexchange Carrier - the organization that carries a call between the caller's service provider and the called party's service provider where the caller's service provider does not serve the area of the called party.

Jeopardy: 

Jeopardy is the condition where an NPA is in danger of running out of available NXXs to use for new telephone subscribers, requiring a freeze on the issuance of further subscriber numbers in that NPA until more NXXs become available.

LEC:

Local Exchange Carrier, the service provider for a caller using a landline or VoIP service, the organization that provides dial tone and carries a call to the called party where they are within the service area of the LEC, or transfers the call to an IXC when the called party is outside its service area.

N versus X:

In the context of a telephone number, N is used to indicate a digit that is restricted to values of 2 through 9, while X indicates an unrestricted digit with values 0 through 9.

NPA:

The area code, or first three digits of the 10-digit telephone number. This document will use both 'area code' and 'NPA' interchangeably, generally with NPA used when discussing technical and implementation issues, and area code being used when discussing issues faced by subscribers and the public.

NPAX:

The new area code, or first four digits of the new 11-digit telephone number. This proposal recommends expansion of the NPA field by 1 digit and provides an expansion of the entire telephone number to 11 digits.

NXX:

The prefix, or digits four through six of the 10-digit telephone number, or first three digits of the subscriber number. This field is to remain unchanged, but is moved to digits five through seven of the new 11-digit telephone number.

SIT tone:

A Special Information Tone (SIT) is a standardized, three-beep audio signal (typically 950/1400/1800 Hz) played before a recorded announcement to indicate a telephone call has failed.

Subscriber number:

The portion of the telephone number following the NPA or NPAX. It remains unchanged at seven digits, but is moved from positions four through ten of the telephone number, to positions five through eleven.

Telephone number:

The entire number of the party to be called, consisting of either

On 10-digit systems, the three-digit NPA, three-digit NXX, and four-digit XXXX. On 11-digit systems, the four-digit NPAX, three-digit NXX, and four-digit XXXX.

VoIP:

Voice Over IP, or telephone service where the call initiates from or terminates via the Internet.

XXXX:

The last four digits of the subscriber number, or line number, digits seven through ten of the 10-digit telephone number. This field is also to remain unchanged, but is moved to digits eight through eleven of the new 11-digit telephone number.

Problem Statement The finite capacity of the current NANP is not a hypothetical concern but an eventual certainty. According to NANPA's October 2025 NANP Exhaust Analysis [NANPA-2025-10], the NANP is projected to exhaust available numbering resources between 2052 and 2060, depending on demand growth rates. The baseline projection, using an average annual CO code demand of 5,213 codes, places exhaustion in 2060. A sensitivity analysis using demand 20% above baseline projects exhaustion as early as 2052. These projections assume a pool of 680 usable NPAs; the remainder of the 800-NPA address space is reserved or unavailable, including 80 NPAs explicitly held in reserve for future NANP expansion — an implicit acknowledgment by the standards community that structural expansion will eventually be required.
This is an even shorter timeline than estimated in , only six months earlier. The current NANP faces several challenges: Finite NPA capacity under existing numbering rules Fragmentation of numbering resources due to allocation practices Growing operational complexity in routing and database systems Long lead times required for major numbering plan changes A long-term solution should address these challenges while preserving fixed-length numbering. Variable-length telephone number schemes are explicitly rejected: they introduce timing-based ambiguity, complicate digit analysis at every layer of the switching and routing stack, increase validation burden across interconnected systems, and create inconsistent user experiences across regions and carriers. Fixed-length numbering is a foundational property of the NANP and must be preserved in any expansion. All feasible approaches to expanding NANP numbering capacity introduce some degree of disruption. The proposed expansion of the NPA is considered the least disruptive option, as it preserves the existing hierarchical structure of the numbering plan and minimizes changes to subscriber numbering and routing semantics.

Design Goals The proposed solution is guided by the following goals: Maintain fixed-length numbering Minimize changes to existing routing logic Preserve compatibility with existing numbering structures

Non-Goals The following approaches are explicitly not considered desirable: Variable-length telephone numbers Region-specific numbering formats Frequent or repeated structural changes to the numbering plan Solutions requiring rapid or "flash cut" transitions

Proposed Expansion Model This document is a proposal to expand NANP numbers from 10 to 11 digits by extending the NPA from three digits to four digits. This ensures that existing fixed-position digit parsing logic can be extended with minimal modification, avoiding the need for timing-based or variable-length interpretation. Existing numbers:

Expanded format:

During initial deployment, the fourth digit added to the NPA to form the NPAX MUST be selected such that it does not conflict with existing digit patterns used to identify the first digit of NXX codes. Under current NANP rules, the first digit of an NXX is restricted to values 2 through 9. By selecting 0 or 1 for the additional NPA digit, the boundary between the expanded NPAX and the following NXX remains unambiguous. This allows existing digit analysis algorithms to distinguish between legacy 10-digit and expanded 11-digit numbers using a simple examination of the fourth digit. Restricting the fourth digit initially to a single value minimizes required changes to routing logic and reduces deployment cost. This property allows existing fixed-position digit analysis logic to be extended with minimal modification, avoiding the need for timing- based disambiguation, interdigit timeout adjustments, or variable- length parsing mechanisms. A single value (0 or 1) SHALL be used consistently across all NPAs during the initial deployment phase to ensure uniform behavior across networks. Uniformity avoids user confusion, simplifies parsing, and prevents mixed national behavior during migration. Example:

Or:

A telephone switching system processes a telephone number using the following logic: Scan fourth digit of number. If 0 or 1, process as NPAX. Else, process as NXX. This proposal preserves the semantic structure of the number. The NPAX field preserves the existing role of the NPA field, whether geographic, overlay, toll-free, or service-specific. NXX is still used as the routing block. XXXX is still the subscriber line number. The widespread adoption of overlay area codes has fundamentally altered the NANP environment. A return to strictly geographic, non-overlapping area codes is no longer practical. The proposed approach assumes the continued existence of overlays and does not attempt to reverse this trend. The designation of 988 as a nationwide service code required the elimination of 7-digit dialing in affected areas, accelerating the transition to uniform 10-digit dialing across the NANP. As a result, this proposal does not impact legacy 7-digit dialing, as that capability has already been largely eliminated. This approach ensures that numbering expansion occurs at the highest level of the NANP hierarchy, avoiding disruption to lower-level components such as routing prefixes and subscriber numbers. This method preserves fixed-field positional parsing, avoiding the need for timing-based digit collection or variable-length interpretation, which are known sources of complexity and error in telephony systems.

Human Factors During and after transition, published numbers SHOULD be displayed in hyphenated 4-3-4 form (e.g., 2130-555-1234). Users will find this format similar to the existing 3-3-4 format, and are expected to adapt to the new format following the patterns observed during the transition to mandatory 10-digit dialing. Contact storage systems, dialing interfaces, and automated dialing features are expected to adapt with minimal modification due to the preserved fixed-length structure.

Routing Considerations Existing routing systems rely on fixed field positions within the NANP number. The proposed expansion preserves the relative position of the NXX and subscriber line number fields, allowing for minimal modification to routing logic. Systems that perform digit analysis MUST be updated to recognize the NPAX format. This includes SS7-based switching systems (the signaling protocols used to route calls across telephone networks), SIP routing platforms, and number portability databases. These updates are limited to recognition of the fourth digit as a format discriminator and do not require changes to downstream routing logic based on NXX or subscriber number.

Potential Misunderstandings Historically, the leading domestic prefix "1" served a toll-alert or toll-access function. It warned the caller, and the network, that the call was being placed outside the local calling area and might incur higher charges. This distinction mattered when local calls were flat-rate or inexpensive while toll calls could be substantially more expensive. That function has diminished in modern wireless, VoIP, and bundled calling environments, where calls are often rated independently of whether the caller dialed a leading "1". Accordingly, this proposal treats the leading "1" as an optional domestic dialing prefix or legacy access convention, not as part of the NANP telephone number. Under this proposal, the NANP subscriber number expands from 10 digits to 11 digits: NPAX-NXX-XXXX Some legacy systems or carrier arrangements may continue to accept or require a leading domestic prefix, commonly "1", before the NANP number. In that case, the dialed digit sequence may contain 12 digits: 1-NPAX-NXX-XXXX However, the leading "1" is not part of the NANP telephone number itself. Many wireless and VoIP systems already accept calls with or without this prefix, and this proposal does not require any change to that behavior.

Transition Strategy A phased transition is recommended:

Phase 0: Infrastructure Readiness Networks and systems are updated to support 11-digit numbers without public announcement. Switching systems MUST be updated to recognize and correctly route NPAX-based numbers during Phase 0. The restriction of the fourth digit to 0 or 1 is bridge logic. It is not intended to be a permanent numbering constraint. During the transition period, it permits legacy 10-digit NANP numbers and expanded 11-digit NANP numbers to coexist without variable-length ambiguity, simply by examining the fourth digit of the telephone number. Once 11-digit dialing becomes mandatory and legacy 10-digit dialing is retired for ordinary call completion, the bridge logic is no longer required. At that point, the fourth digit of the NPAX may be opened to additional values under the ordinary NANP assignment process. There SHOULD be some cross-network communication system such as a website, a mailing list, a help desk, and/or other method for parties involved in the conversion to report progress and to obtain information helpful in diagnosing problems, issues and events that may require special attention or otherwise require additional resources for resolution. This SHOULD be provided or operated by a neutral third-party.

Phase 1: Dual-Format Acceptance Both 10-digit and 11-digit dialing are accepted by all CPs, IXCs, and LECs. All originating and terminating networks MUST accept both formats.

Phase 2: User Notification Phase 2 is implemented as two segments.

Segment 1 In Segment 1 of Phase 2, LECs, CPs, IXCs, and regulatory authorities MUST publicize the implementation of the expansion of the NPA to an NPAX, where the area code is expanded to four digits, and the telephone number to eleven digits. An important highlight of the announcement SHOULD emphasize that there will be no change to the subscriber number. It SHOULD also state the date Segment 2 will begin and the date that phase 3 will begin.

Segment 2 In Segment 2 of Phase 2, Intercept messages SHALL be imposed on callers dialing a 10-digit phone number, and such message SHALL inform callers dialing telephone numbers using the current 10-digit format of upcoming requirements, MAY inform them of the digit they need to append to the area code, and SHOULD state the date when dialing the new 11-digit number will be required. The call SHALL still complete.

Phase 3: Mandatory Expansion 11-digit dialing becomes required. Callers dialing the old format 10-digit number SHALL be presented with an intercept message beginning with a SIT tone and an announcement that they must dial the new 4-digit area code. The message MAY announce the additional digit that MUST be dialed. The call SHALL NOT complete, and SHALL be treated equivalently to dialing an invalid number.

Phase 4: Full Expansion The fourth digit of the NPA is opened to all values 0 through 9, increasing numbering capacity. Phase 4 MUST NOT begin until 10-digit dialing has been retired for ordinary call completion. At that point, all NANP numbers are parsed as NPAX-NXX-XXXX, and the fourth digit is no longer needed to distinguish legacy and expanded formats.

Alternatives Considered The following alternatives were evaluated:

Further subdivision of number pooling blocks Further subdivision of pooling blocks provides only limited extension while increasing database and administrative complexity.

Expansion using only reserved NPA ranges (e.g., N9X) If the rest of the available NPAs are exhausted, this becomes a stop- gap measure until this or some other planned expansion of the telephone number to 11 digits.

Overlay NPAs Originally each NPA covered one region exclusively. As more telephone numbers were needed, more NXXs were added until no more were available. The answer at that point is to split the NPA, take about half the NXXs that were geographically adjacent to each other, and assign them to the new NPA. The advantage was the subscriber number did not change, so local seven-digit dialing was unaffected, and the subscriber simply had to advise people that their area code had changed. This practice worked when regions were large and the remaining regions after the split are of a reasonable size. When they are city-sized or smaller, splitting NPAs produces a point of diminishing returns, where an NPA might only be part of a city. The switch to overlays alleviated this problem as now the combined number pool of both NPAs is available for the entire region. It also ends the dilemma of an NPA in jeopardy status being split, with one NPA having more than sufficient available NXXs and the other remaining in jeopardy. Overlays were inevitable and solved the problem of an NXX surplus/starvation NPA split result dilemma. While overlays are useful, and it is very likely new NPAs will be added as overlays to existing regions, they won't be enough to solve the problem when it is not NXXs that are in jeopardy, but NPAs.

Variable-length numbering schemes These approaches introduce significant implementation complexity, increase validation burden across systems, and may negatively affect user perception of numbering uniformity. These approaches either provide limited long-term benefit or introduce undesirable complexity.

Expansion Of NXX To NXXX The expansion of the subscriber number to 8 digits by increasing the size of the NXX to four digits was considered, but it creates an even larger disruption: The number of NXXs in an NPA rises from slightly under 800 to nearly 8,000. It would vastly increase the size and complexity of local number portability databases It would also increase the number and size of call routing tables Third parties would have to update software for holding much larger number ranges The number of potential telephone numbers in an area code rises from around 7,000,000 to nearly 70,000,000 In most regions this would cause each area code in the state to be many times greater than the entire population of the region served by that NPA. Much of the additional capacity would be unusable or wasted.

Expansion Of XXXX To XXXXX The expansion of the line number to 5 digits adds even more complexity and potentially even greater added costs than expanding the NXX to 4 digits: Even larger number portability databases, as each NXX expands by a factor of 10 Local switches have to handle not potentially 10,000 lines for each NXX they service, but 100,000 It is entirely possible switch hardware cannot support this large a number pool, either rewiring replacement or upgrading expensive switching equipment. It may require splitting NXXs onto multiple switches and require even more routing changes to accommodate. In heavily populated urban areas it might require acquisition of  additional expensive switches, real estate, and buildings.

Operational Considerations The proposed expansion is designed to minimize impact on: Call routing systems Number portability databases Inter-carrier signaling However, significant updates would be required in: Customer-facing systems Validation logic Legacy equipment and embedded systems A question that may arise is "Why not allow the full number range of 0-9 in the fourth digit of the telephone number to be activated immediately, rather than the current proposal to initially only permit a single digit?" The rationale is cost and complexity. Initial deployment using a single digit minimizes required routing changes. This proposal acknowledges that significant costs would be involved in moving to an 11-digit telephone number. Eventually, the change must happen. The fact remains, initially implementing only one digit generates the least amount of cost increase, as only the routing logic of the fourth digit of the telephone number is required to be changed. Later, when digits 2-9 are enabled, the code required to check the fourth digit can then be eliminated. Thus, this also reduces the complexity involved in making this change.

Backwards Compatibility Risks There will need to be lead time to account for, and attention placed on informing owners of systems that may need to be replaced because of incapacity to update them to use the new format telephone number, such as systems using: Hard-coded 10-digit fields Regular expression validation failure Embedded devices Emergency equipment that sends "final warnings" or notifications need to be considered: Elevator telephones Audible Burglar alarms Silent alarms Credit/debit card processing terminals in places where Internet connections are unavailable Roadside motorist assistance telephones Civil emergency response centers will have critical need to make certain proper expansion and adjustment is done for: 911/E-911 routing PSAP systems ALI/ANI databases Number portability and carrier identification databases must be adjusted to compensate for this change: LNP databases are massive, and may require updates to database schemas and query logic in both SQL and NoSQL implementations Key lookup structures are dependent on current NPA-NXX format One advantage this proposal provides is it requires no change to NXX format, preserving existing LNP granularity.

Benefits The current NPA format allows a maximum of 800 NPAs to be implemented (200-999). However, practical considerations reduce this in several ways: X11 codes (211, 311, 911 etc.) are unavailable 988 as an additional N11-style number (and possibly others in the future) will reduce the supply further N9X was reserved for future expansion. Given these constraints, the maximum number of NPAs is probably more like 700. While this is a large number, it eventually will be exhausted, possibly within the foreseeable future. Expansion of area codes to add an extra digit, and later full expansion to 11-digits expands the numbering range by a full factor of magnitude, to 8000 possible NPAXs. Assuming similar carve-outs are used: N11X is reserved to prevent confusion 988X is also reserved Other similar service codes to 988 (200, 766, 322, 433 etc) are created, and those code ranges are restricted, e.g. 200X, 322X, 433X N9XX is reserved for future expansion It still leaves a huge pool of available NPAXs. If the X11X, 988X, and 10 additional service code code blocks are reserved, in addition to N9XX, we have 72 NPAXs restricted for N11X protection 110 NPAXs restricted for 988X protection and 10 additional service code blocks 800 NPAXs reserved for N9XX expansion Leaves more than 7,000 potential NPAXs available for assignment. This represents an approximate order-of-magnitude increase in addressable numbering capacity compared to the current NANP structure.

Economic Considerations I am not ignoring that the change is going to be massive, and expensive. This is why it is important to start thinking about the issue well in advance of when action becomes mandatory, and to begin planning this change long before it is necessary. An orderly transition on a long timetable with reachable milestones and progress goals will be easier and less costly than an "under the gun" rushed change because the deadline is approaching and we can't wait. The history of infrastructure transitions is littered with examples of "we'll deal with it later" becoming "we're dealing with it in crisis mode at enormous cost." The two closest analogies in the tech world are instructive: The Internet address space IPv4 exhaustion is the cautionary tale. The internet community knew for decades that 32-bit addresses would run out. IPv6 was standardized in 1998. Here we are in 2026 and the transition is still incomplete — largely because nobody acted until addresses were actually scarce, by which point the installed base was so enormous that migration became enormously painful and expensive. The NANP is in a similar position today: there's still time to plan, but that window won't stay open forever. The problem caused by the near-universal use of six-digit date fields in computer systems resulted in the "Y2K" crisis when people realized date calculations were going to fail when the year 2000 arrived, possibly in a catastrophic fashion. While extreme effort prevented a disaster scenario, it still came at enormous cost, because the work had to be done under severe time constraints. This would not have been necessary if it was started earlier. Articles in trade magazines as far back as 1985 were warning about the upcoming problem, which was mostly ignored. Until it couldn't be. The 20- to 40-year timeframe for the upcoming exhaustion is the sweet spot for this kind of change: long enough that a careful, phased transition is feasible, short enough that "we'll get to it" is genuinely dangerous. The 20–40 year estimate is not a reason to wait, but the reason to start now.

Advantages to Starting Early With 20-35 years of runway: Vendors can absorb changes into normal product refresh cycles rather than emergency patches Carriers can budget capital expenditure in advance rather than emergency spending Regulators can run proper notice-and-comment processes Embedded systems — elevator phones, alarm dialers, card terminals — can be replaced through natural attrition rather than forced recall The standards process itself can work at a measured pace with time for revision and refinement Training, documentation, and public communication can be thoughtful rather than rushed With five years of runway, every single one of those becomes a crisis.

Cost Considerations Of Methods Used Incremental approaches distribute cost over time but increase long-term complexity. A planned expansion incurs higher initial cost but may reduce cumulative cost and operational burden. Early planning enables gradual transition and reduces the risk of emergency implementation.

Billing and Rating Impact Carriers price call charges (including call origination and termination payments) on NPA-NXX LATA boundaries Other than increasing the length of the NPA and temporarily carrying duplicate records (one for the old 3-digit NPA, and one for its replacement NPAX during phases 1 through 3 (much of which can be automated) these impacts are expected to be minimal due to preservation of the NPA-NXX structure used in existing billing and rating systems.

Stakeholder Impact

Security Considerations Changes to numbering formats may impact fraud detection systems, call validation mechanisms, and authentication processes. These impacts SHOULD be evaluated during implementation planning. Number spoofing detection systems, including but not limited to STIR/SHAKEN authentication to take into account both the current, and replacement numbers. Call authentication frameworks, robocall enforcement tools, and carrier reputation systems all embed assumptions about 10-digit number formats. Call authentication assumptions MUST be reviewed and updated to ensure compatibility with both legacy and expanded numbering formats. This represents an approximate order-of-magnitude increase in addressable numbering capacity compared to the current NANP structure.

Transition Governance Governance is arguably the hardest part of any NANP change. Prior transitions (e.g., the 1995 area code relief plan, the 988 rollout) would be instructive in preparation, management, and implementation of any solution to this issue. One or more coordinating authorities MUST be designated to manage key aspects of the transition. These include: Whether the NPAX flag digit in position 4 of the telephone number is 0 or 1 Timeline for start and implementation of each phase and segment of the upgrade plan Who will be responsible for enforcing compliance with all mandates? This could be a single organization, or a cooperative arrangement of regulatory and operating companies (Carriers, Canada's CRTC, NANPA, Regulatory authorities in other jurisdictions, U.S. FCC, etc.)

Transition Difficulties Not all parties involved in the transition will necessarily act as expeditiously as possible. Concerns over depreciation or amortization of existing equipment and/or  software will be a serious concern to various organizations and responsible  individuals. This may result in compatibility problems with respect to "Long tail" legacy systems Private Branch Exchange (PBX) systems International interoperability lag As a result, partial deployment conditions may persist long after others are fully ready for the changes as a result of the implementation of 11-digit telephone numbers.

International Considerations The proposed 11-digit format remains compatible with the E.164 maximum length of 15 digits. Coordination with international carriers and regulatory bodies is required. This change poses no impact to global numbering compatibility It fits into the existing +1 country code model No changes to the E.164 country code (+1) are required. Coordination among over 25 international jurisdictions, state and provincial regulators, and the ITU will need to be taken into account.

IANA Considerations This document has no IANA actions.

Conclusion Expansion of the NANP to 11 digits represents a viable long-term solution to numbering exhaustion. Early commitment to a transition plan is essential to enable a controlled and gradual transition, and
avoid time-constrained or emergency implementation. Expansion of the NANP to 11 digits is not an immediate necessity — but it is an eventual certainty. The question is not whether this transition will happen, but whether it will be managed or improvised. With a projected exhaustion window of 2052 to 2060, the NANP community is in a position that infrastructure planners rarely enjoy: enough lead time to do this properly. A carefully designed, phased transition executed over 10 to 20 years allows vendors to absorb changes into normal product refresh cycles, carriers to plan capital expenditure in advance, embedded systems to be replaced through natural attrition, and the public to adapt gradually rather than abruptly. Regulatory processes can proceed at a measured pace. Standards can be refined. Mistakes can be caught and corrected before they propagate. That window is not permanent. The history of infrastructure transitions offers two instructive examples. Y2K was resolved successfully — but only because the industry mobilized with sufficient lead time, and it was still extraordinarily expensive and stressful with years to spare. IPv4 address exhaustion is the alternative outcome: a problem understood for decades, deferred until it became acute, and still incompletely resolved thirty years after IPv6 was standardized. The NANP does not have to follow either path exactly. The lead time available today makes a third outcome possible: a transition that is planned deliberately, implemented gradually, and completed before urgency drives the agenda. Early evaluation and commitment to a structural solution — of which this proposal is one candidate — is the prerequisite for that outcome. Given the long lead times required for numbering plan changes, the time to begin is now, while beginning is still a choice.

In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. International Telecommunications Union North American Numbering Plan Administrator North American Numbering Plan Administrator This RFC gives the list, as best known, of all common Internet domains and the conversion between specific country telex answerback codes and Internet country domain identifiers. It also lists the telex code and international dialing code, wherever it is available. It will also list major Internet "Public" E-Mail addresses. This memo provides information for the Internet community. It does not specify an Internet standard.

Changelog draft-00: Initial Release draft-01: correct misspelling: allowsexisting -> allows existing Explain drawbacks of some alternative strategies Adjust line lengths to improve ease if editing, to take advantage of kramdown-rfc and xml2rfc automatic reformatting draft-02: add executive summary clarify that some actions are temporary in nature ("bridge logic") while the transition from 10-to 11-digits is in progress. give examples of inaction and why it should be avoided