United States area codes and phone numbers. Whitepages provides the most comprehensive search statistics and results for telephone numbers in North America. Each US area code may contain up to 7,919,000 phone numbers, and formats are always NPA-NXX-XXXX:
NPA = Area code assigned to a Numbering Plan Area,
NXX = Prefix or „exchange” assigned to a central office,
XXXX = Local number or „subscriber number”.