Area Code and Central Office Code Assignments
The assignment and administration of Area Codes and Central Office Codes used in the Public Switched Network is the responsibility of the North American Numbering Plan Administrator (NANPA). Briefly stated, this entity administers the FCC's rules regarding numbering matters.
Information concerning Area Code assignments is available at the NANPA's website, http://www.nanpa.com/area_codes/index.html and a number of commercial websites, such as http://www.areacodelocations.info/.
Information concerning Central Office Code requests and assignments can be found at http://www.nanpa.com/number_resource_info/co_codes.html.