North American Numbering Plan (NANP)

The North American Numbering Plan (NANP) is a telephone numbering plan used by most countries in North America, including the United States, Canada, and parts of the Caribbean. It was first implemented in 1947 and is administered by the North American Numbering Plan Administration (NANPA), a service of Neustar.

The NANP uses a 10-digit numbering system, divided into three parts: the Numbering Plan Area (NPA) or area code, the Central Office (CO) code, and the Line Number. The format is NXX-NXX-XXXX, where N is any digit from 2 through 9, and X is any digit from 0 through 9.

Area codes are the first three digits of a phone number and identify a specific geographic region or mobile carrier. Originally, area codes were assigned based on geographic location, but with the growth of mobile and VoIP services, this is no longer the case.

The central office code, the second set of three digits, identifies a specific central office or exchange within the area code. This code was originally assigned based on the location of the central office, but like area codes, this is less relevant with modern telecommunications.

The last four digits of a phone number are the line number, which identifies a specific telephone line or device within the central office.

When dialing a NANP number from outside the region, the international access code for the country is dialed first, followed by the country code for the NANP, which is 1, and then the 10-digit NANP number.

The NANP has undergone several changes to accommodate the growth in the number of telephone lines and the introduction of new services. This includes the addition of new area codes through various methods such as splits, overlays, and reserved area codes.

As technology continues to evolve, the NANP will need to adapt to new challenges, such as the increasing use of VoIP and the potential exhaustion of available 10-digit numbers.