Area Codes
In 1947, Bell Laboratories and AT&T developed the North American Numbering Plan (NANCP) for telephones in the United States and Canada. The first codes given out were to states that only had need for one area code (Florida, Delaware, and Connecticut)—these three-digit area codes had a 0 for the middle number. States needing more than one area code received three-digit numbers with 1 for the middle number.
Over the years, a number of potential coding programs had been examined and discarded by the Post Office Department, in response to an exploding mail industry. Finally, in 1963, the Department selected a system created by department officials, and, on July 1, 1963, zip codes were put into use.