Early in the 20th century, the American and Canadian telephone industry had established criteria and circuits for sending telephone calls across the vast number of local telephone networks on the continent to permit users to … See more

Most automatic dial switching systems were designed since the early 1920s to provide service for up to ten-thousand subscriber lines. … See more

The number of central offices that could be effectively installed in a numbering plan with two letters and one digit for the central office code was … See more

For several years, area codes could only be used for Operator Toll Dialing by long-distance operators on routes between toll offices equipped … See more

Building a nationwide network in which any telephone could be dialed directly required a systematic numbering system that was easy to understand and communicate. Local telephone numbers varied greatly across the country, from two or three digits in … See more

By 1945, initial concepts for a nationwide numbering plan anticipated a division of the continent into between fifty and seventy-five numbering plan areas. For this size of the network, a unique two-digit code for each numbering plan area (NPA) would have been … See more

• List of future North American area codes
• List of North American Numbering Plan area codes See more