Current System
Developed in the 1940s, and first implemented in 1951 by AT&T Corporation, the NANP set out to simplify and facilitate direct dialing of long distance calls. Area code 201 was the first implemented under the plan. The NANP initially applied only to the U.S. and Canada, but at the request of the British Colonial Office, it was expanded to Bermuda and the British West Indies (including Trinidad and Tobago), because of their historic telecommunications administration through Canada as parts of the British Empire — and also their continued associations with Canada, especially during the years of the telegraph and the All Red Line system.
Despite the "North American" name of the calling plan, not all North American countries participate in NANP. Mexico, the Central American countries and some Caribbean countries (Cuba, Haiti, and the French and Dutch-speaking Caribbean, though Dutch-speaking Sint Maarten joined the NANP in September 2011) are not part of the system. The only Spanish-speaking sovereign nation in this plan is the Dominican Republic. Mexican participation was planned, but implementation stopped after two area codes were put into use (Mexico City and northwestern Mexico); these ended in 1991 when Mexico withdrew from the NANP.
Saint Pierre and Miquelon (+508) and Greenland (+299), both North American possessions of European Union nations, use non-NANP codes which are independent of their respective home countries (+33 France and +45 Denmark).
The NANP is administered by the North American Numbering Plan Administration (NANPA).
Current NANP number format can be summed up via the following:
- +1-NPA-NXX-xxxx
| Component | Name | Number ranges | Notes |
|---|---|---|---|
| +1 | ITU country calling code | "1" is also the usual trunk code for accessing long-distance service between NANP numbers. In an intra-NANP context, numbers are usually written without the leading "+" | |
| NPA | Numbering Plan Area Code | Allowed ranges: for the first digit, and for both the second and third digits. | Covers Canada, the United States, parts of the Caribbean Sea, and some Atlantic and Pacific islands. The area code is often enclosed in parentheses. |
| NXX | Central Office (exchange) code | Allowed ranges: for the first digit, and for both the second and third digits. | Often considered part of a subscriber number. The three-digit Central Office codes are assigned to a specific CO serving its customers, but may be physically dispersed by redirection, or forwarding to mobile operators and other services. |
| xxxx | Subscriber Number | for each of the four digits. | This unique four-digit number is the subscriber number or station code. |
For example:
- (234) 235 5678 is valid
- (123) 234 5678 is invalid, because NPA cannot begin with "0" or "1"
The country calling code for the NANP is +1. In international format, an NANP number should be listed thus: +1 301 555 0100 (example using the original area code for Maryland). "1" is also the code often used to make direct-dialed long-distance calls within the NANP.
Each three-digit area code may contain up to 7,919,900 unique phone numbers:
- NXX may begin only with the digits, providing a base of 8 million numbers: ( 8 x 100 x 10000 ) .
- However, the last two digits of NXX cannot both be 1, to avoid confusion with the N11 codes (subtract 80,000).
- Despite the widespread usage of NXX "555" for fictional telephone numbers — see 555 (telephone number) — today, the only such numbers specifically reserved for fictional use are "555-0100" through "555-0199", with the remaining "555" numbers released for actual assignment as information numbers (subtract 100).
- Several other NXX prefixes are generally not assigned: the home area code(s), adjacent domestic area codes and overlays, area codes reserved for future relief nearby, industry testing codes (generally NXX 958 and 959) and special service codes (such as NXX 950 and 976).
Read more about this topic: Area Codes In The United States
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