Trunk vs Toll

In the US, under the purview of the Bell System, local telephone calls were free except in a few big cities, and the term toll was adopted for long distance calls because they were subject to a toll.

In the UK all calls were chargeable and the term trunk was adopted for long distance calls. Initially all trunk calls had to be pre-booked and the operator called the subscriber back when the call could be put through. In 1921 the first [http://www.btplc.com/Thegroup/BTsHistory/1912to1968/1921.htm toll exchange] was opened which allowed the shorter distance trunk calls to be connected while the subscriber waited. The name toll was probably taken from US usage.

In the London telephone area calls to subscribers on non-director exchanges within local call charging range of the London director exchange area were carried by tandem exchange 'Toll A'; a subscriber would dial a prefix code, then the number of the other subscriber on the fringe non-director exchange. Calls from fringe non-director exchanges to numbers within the director area were passed in two ways. For those to director exchanges near the area boundary adjacent to the non-director exchange, subscribers were given codes to dial, and told to follow the code with the numerical portion of the other subscriber's number. For director exchanges remote from the area boundary, the subscriber was told to dial '7', to wait for a second dialling tone, and to follow this with the whole of the other number. These calls were handled by tandem exchange 'Toll B'; from here the second dialling tone originated. To have a second dialing tone in this way was very unusual on the PSTN in the UK, although the French PTT had a similar instruction for when their customers made international calls.

The distinction between trunk and toll became irrelevant when subscriber trunk dialling (STD) was introduced.