Operator Toll Dialing was a project and method used by the Bell System in the USA and Canada to automate the switching and billing of long distance calls in the public switched telephone network (PSTN). 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 The system was implemented in the USA beginning in 1946 and was gradually superseded by Direct Distance Dialing (DDD) by 1965.
Telephone administrations in other countries implemented similar programs, such as in the United Kingdom, which led to Subscriber Trunk Dialling (STD).