Operator Toll Dialing
Operator Toll Dialing was a project and method used by the Bell System in the US and Canada to automate the switching and billing of long-distance calls in the public switched telephone network. The program was initiated by 1945, at which time ca. 5% of the 2.7 million toll board calls per day were handled by this method.
Operator Toll Dialing eliminated the need for intermediate and inward operators to complete toll calls to distant central offices. Initially this system involved step-by-step routings to set up each circuit, but later was improved by the development of area codes with machine translation which helped to standardize dialing across the network. The system was implemented in the US beginning in 1946. In 1947, it was integrated with the newly devised North American Numbering Plan which assigned unique area codes that served as routing codes for calls between numbering plan areas.
Operator Toll Dialing was gradually superseded by direct distance dialing, in which the customer dialed the area code followed by a seven-digit telephone number. Beginning in 1951 on a limited basis, DDD was not fully implemented until the 1970s.
Telephone administrations in other countries implemented similar programs, such as in the United Kingdom, which led to subscriber trunk dialling.
