We recommend that you start with the source, at www.nanpa.com. NANPA is the authority on planned changes in area codes (NPAs). Since plans do change, you have to check in periodically to stay current. State laws generally require that the public be given notice of impending changes and be given the right to comment. It is not uncommon for planned changes to be suspended or modified as a result of the public-hearing process. The NANPA Web site has charts summarizing planned new NPAs as well as NPAs already in use. It also has Planning Letters detailing the timetable and procedures for each planned change.

Need some background information? Having trouble decoding the technical jargon? Some phone-company sites such as www.pacbell.com are excellent places to learn such terms as area code relief, permissive dialing, pooling, local number portability, and other arcana.