The North American Numbering Plan has been in use since 1947, and has endured that time with only minor changes. So far, unlike many other nations, it has not been necessary to lengthen phone numbers to accommodate expansion. To date, the accommodation of demand has been achieved by adding area codes (NPAs) for relief, either as a split or as an overlay. The North American Numbering Plan (NANP) is a system for three-digit area codes and seven-digit telephone numbers that direct telephone calls to particular regions on a public switched telephone network (PSTN), where they are further routed by the local network. ... 1947 (MCMXLVII) was a common year starting on Wednesday (the link is to a full 1947 calendar). ... A telephone number is a sequence of decimal digits (0-9) that is used for identifying a destination telephone line in a telephone network. ... A telephone numbering plan is a system that allows subscribers to make and receive telephone calls across long distances. ...

Although the plan provides for a potential of 6,400 million telephone numbers, a considerable percentage of these numbers will remain unused when the last available NPA code is assigned, as thousands of numbers will not be in use in exchanges that serve only a small population center, the exchange being served by a single NPA-NXX combination in non-competitive markets (and more combinations in the unlikely event that such a small market has competitors).

As a result, as the supply of unassigned NPA codes dwindles, it will be necessary for telephone carriers in North America to implement expansion beyond the current 10 digit format. Expansion has been a matter of discussion by industry forums for several years, and although a recommendation has been made, that expansion plan format has not been approved by the regulatory authorities (the Federal Communications Commission and the Canadian Radio-Television and Telecommunications Commission), and the regulators may choose a different expansion plan format. The FCCs official seal. ... The Canadian Radio-television and Telecommunications Commission (CRTC, in French Conseil de la radiodiffusion et des télécommunications canadiennes) was established in 1968 by the Canadian Parliament to replace the Board of Broadcast Governors. ...

The industry forum considered dozens of potential options and identified the difficulties with each option.

Current industry recommendation

The telephone industry's current recommendation assumes first that mandatory dialing of all ten digits is required to complete telephone numbers, even for a local call, throughout the North American Numbering Plan area, which includes many Caribbean and Pacific territories and nations.

The plan proposes the insertion of two zeroes or two ones between the NPA and the Central Office Code (commonly referred to as an NXX in industry jargon), to produce twelve-digit numbers. The plan further proposes that the United States would use either 00 or 11, while Canada would use the other, in order to allow customers to distinguish countries by use of these digits, which do not appear at the beginning of the 12-digit number.

Under this proposal, the N9X format NPA codes, which are currently reserved from assignment, would be released and be available for normal assignment for code relief and other purposes.

Other proposals

Proposals that utilize the reserved N9X format codes for expansion include the following proposals:

N9XX, with no change to the remainder of the phone number, would expand numbers to eleven digits overall. A 9 would be inserted as the new second digit of all area codes (e.g. 212 would become 2912, 916 would become 9916). Permissive dialing would be allowed, as exchange equipment, on detecting a 9 as the second digit of the area code, would respond appropriately to expect 11 digits, or 10 in the absence of a 9 in that position.

The drawback of this plan is that the same pace of area code relief would be required, although there would be 7000 new area codes available.

N9XX, with a new initial digit in front of the last seven digits of the phone number, would expand numbers to twelve digits overall. As with the above plan, a 9 would be inserted as the new second digit of all area codes. The problem would occur with permissive dialing of local calls where the area code is not presently required (areas with no overlay in effect). If the added digit were 3, for example, numbers that already begin with a 3 would present a problem, probably resolved using either a "time-out" if the customer only dials seven digits, or a flash-cut to mandatory eight digit dialing.

The advantage of this plan is that the number of available central office prefixes is increased nearly ten fold. Under those conditions, even the fastest growing NPA codes would not require relief for many years, ushering in a period of stability in the North American Numbering Plan (as happened from 1962 to 1981, when only two new codes were added). 1962 (MCMLXII) was a common year starting on Monday (the link is to a full 1962 calendar). ... 1981 (MCMLXXXI) was a common year starting on Thursday of the Gregorian calendar. ...

See also

• North American Numbering Plan