North American Numbering Plan

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The North American Numbering Plan (NANP) was developed in 1947 by AT&T and Bell Laboratories in response to a requirement for a standardized numbering plan for Direct Distance Dialling (DDD). This development allowed long distance calling without the need for operator assistance. Originally, the plan created 86 geographic areas, each with its associated three digit Numbering Plan Area Code (NPA). The plan allowed for expansion to 144 areas plus eight N11 codes and eight N00 Service Access Codes (SAC). With the advancement of switching technology, when the original 144 NPAs exhausted in 1995, the NANP was expanded to 792 codes (some of these include reserved number for expansion, etc.).

The NANP conforms to the International Telecommunications Union Recommendation E.164, the international standard for numbering plans. All countries assigned the ITU Country Code 1 for their Public Switched Telephone Network are members of the NANP. These countries are Canada, United States including its territories (American Samoa, Guam, Northern Mariana Islands, Puerto Rico and United States Virgin Islands), Bermuda and many Caribbean nations, including Anguilla, Antigua and Barbuda, Bahamas, Barbados, British Virgin Islands, Cayman Islands, Dominica, Dominican Republic, Grenada, Jamaica, Turks and Caicos Islands, Montserrat, Saint Kitts and Nevis, Saint Lucia, Saint Vincent and the Grenadines, Sint Maarten, Trinidad and Tobago.

NANP numbers are ten digits in length, and they are in the format NXX-NXX-XXXX, where N is any digit 2-9 and X is any digit 0-9. The first three digits are called the numbering plan area (NPA) code, often called simply the area code. The second three digits are called the central office code or prefix. The final four digits are called the line number.

Over time the NANP grew to include other Numbering resources. All NANP numbering resources, excluding SAC 600 and and non-US geographic Central Office Codes are administered by the North American Numbering Plan Administrator (NANP-A), which is currently Somos, Inc. One of the functions of the CNA is to assist NANP-A in the administration of numbering resources assigned to Canadian entities. The CNA acts as a liaison between the Canadian telecommunications industry and NANPA and ensures that Canadian applications meet Canadian Regulatory requirements.

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