Overview#Number Plan Area (National Destination Code or often referred to as Area Code or city code) is a numeric routing Code within a specific Telephone Numbering Plan which has been divided into regional service areas.
Number Plan Area is often part of a Telephone Numbering Plan which subdivide their territory of service into geographic regions designated by a prefix which is a set of digits forming the most-significant part of the dialing sequence to reach a telephone subscriber.
Number Plan Area concept was first developed for Operator Toll Dialing of the Bell System in the early 1940s, which preceded the North American Numbering Plan (NANP) of 1947. The North American Numbering Plan (NANP) divided the North American service territories into Number Plan Areas (NPAs), and assigned to each NPA a unique numerical prefix, the Number Plan Area code, which became known in short-form as Area Code.
Number Plan Area is prefixed to each telephone number issued in its service area.North American Numbering Plan the Allowed ranges for Number Plan Area for the National Destination Code (Area Codes) are:
- (2–9) for the first digit
- (0-9) for the second
- (0-9) third digit
When the second and third digits of a National Destination Code are the same, that code is called an Easily Recognizable Code (ERC) which designate special services; e.g., 888 or 800 for toll-free service.
North American Numbering Plan is not assigning area codes with 9 as the second digit.