These countries include the United States and its territories, Canada, Bermuda, Anguilla, Antigua & Barbuda, the Bahamas, Barbados, the British Virgin Islands, the Cayman Islands, Dominica, the Dominican Republic, Grenada, Jamaica, Montserrat, St. Kitts and Nevis, St. Lucia, St. Vincent and the Grenadines, Trinidad and Tobago, and Turks & Caicos.
Regulatory authorities in each participating country have plenary authority over numbering resources but the participating countries share numbering resources cooperatively.
AT&T developed the North American Numbering Plan in 1947 to simplify and facilitate direct dialling of long distance calls. Implementation of the plan began in 1951.
The international Telecommunications Union (ITU) assigned country code "1" to the NANP area. The NANP conforms with ITU Recommendation E.164, the international standard for telephone numbering plans.
NANP numbers are ten-digit numbers consisting of a three-digit Numbering Plan Area (NPA) code, commonly called an area code, followed by a seven-digit local number. The format is usually represented as
where N is any digit from 2 through 9 and X is any digit from 0 through 9.