Operator Toll Dialing

Operator Toll Dialing was a toll-switching and routing system used by the Bell System in the US and Canada that automated the switching and billing of long-distance calls.[1] The method evolved from the General Toll Switching Plan of 1929 and was initiated by 1945, at which time ca. 5% of the 2.7 million toll board calls per day were handled by this method.[2]

Operator Toll Dialing eliminated the need for intermediate and inward operators to complete toll calls to distant central offices. Initially this system involved stepwise routing from one toll center to another one logically closer to the destination to set up each circuit.

In 1947, Operator Toll Dialing benefitted from the newly devised nationwide numbering plan that established the original North American area codes and evolved into the North American Numbering Plan. This assigned unique area codes to the newly created numbering plan areas (NPAs), that first served as destination routing codes in Operator Toll Dialing, replacing operator use of trunk codes different at each toll switching center. Instead, switching system were supplemented with apparatus for machine translation of the area codes to location-specific trunk codes.

Operator Toll Dialing was gradually superseded by direct distance dialing (DDD), in which customers themselves dialed an area code followed by a seven-digit telephone number. Activated in 1951 in Englewood, NJ, on a trial 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 (STD).