North American Numbering Plan

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.

Back to Top