The North American Numbering Plan (NANP) divides the territories of its members into geographic numbering plan areas (NPAs). Each NPA is identified by one or more numbering plan area codes (NPA codes, or area codes), consisting of three digits that are prefixed to each local telephone number having seven digits. A numbering plan area with multiple area codes is called an overlay. Area codes are also assigned for non-geographic purposes. The rules for numbering NPAs do …