areacode

An area code is a segment of a telephone number used to designate a geographic region or service area within a national or international numbering plan. Area codes help route calls through the network to the correct local exchanges and, in many systems, are dialed before the local subscriber number.

In the North American Numbering Plan (NANP), area codes are three digits, followed by a three-digit central office code and a four-digit line number, written as NXX-NXX-XXXX. People often present the area code in parentheses when dialing domestically, e.g., [phone]. Within the NANP, some regions use ten-digit dialing even for local calls, and area codes can be geographic or non-geographic overlays created to supply additional numbers.

Internationally, area code length and structure vary. The international standard E.164 defines the overall number format and maximum length, with a country code preceding a national number that may include an area code. The exact dialing rules depend on each country’s numbering plan and practices.

History and evolution: Area codes were introduced in the mid-20th century to enable automated switching and scalable routing as telephone networks expanded. As populations grew and mobile and VoIP services increased demand for numbers, many regions adopted overlays—adding new area codes for the same geographic area—instead of adopting new geographic splits. This often leads to mandatory ten-digit dialing even for local calls.

Impact: While area codes often indicate a region in many numbering plans, mobile numbers can retain their area codes after moves. In some contexts, area codes also carry branding or regional identity beyond strict geography.