Telephone numbering plan

A telephone numbering plan is a system used in telecommunications to give telephone numbers to customers and to route telephone calls in a telephone network. A closed numbering plan imposes a fixed length to numbers, such as in North America (10-digit). An open numbering plan may have telephone numbers that vary in length.
A dial plan establishes the type of telephone number in a given area. This includes country codes, access codes, area codes and all combinations of digits dialed. For instance, the North American public switched telephone network (PSTN) uses a phone numbers with a 3-digit area code and a 7-digit telephone number.