Trunk Versus Toll Telephony
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Trunk and toll calling were two alternative methods of charging customers for long-distance calls in the United Kingdom in the first half of the 20th century. The distinction became obsolete with the introduction of
subscriber trunk dialling Subscriber trunk dialling (STD), also known as subscriber toll dialing, is a telephone numbering plan feature and telecommunications technology in the United Kingdom and various Commonwealth countries for the dialling of trunk calls by telephon ...
(STD).


History

In the UK, local as well as long-distance telephone calls were chargeable to the caller and the term trunk calling was adopted for long-distance calls. Initially a ''trunk call'' had to be booked in advance and a
switchboard operator In the early days of telephony, companies used manual telephone switchboards, and switchboard operators connected calls by inserting a pair of phone plugs into the appropriate jacks. They were gradually phased out and replaced by automated syste ...
called the subscriber when the call set-up was completed; a process known as 'delay working'. Due to increasing demands for trunk calls from London and the associated delays in connecting them, calls to exchanges adjacent to the London director area were transferred to a new toll exchange opened on 17 September 1921. Calls to toll area exchanges were connected on-demand whilst the originating subscriber waited, thus improving service and reducing operator costs. The London Toll Area boundary was extended in 1923 and again in 1928, so that eventually Southampton, Portsmouth, Reading, Bedford, Colchester and the whole of Kent and Sussex were included. The system was later introduced to other large cities and remained in use until the late 1950s when, with the advent of Subscriber Trunk Dialling, Toll was eventually phased out. The name ''toll'' was probably taken from US usage. In London, telephone calls to subscribers who were not serviced by
Director telephone system The director telephone system was a development of the Strowger or step-by-step (SXS) switching system used in London and five other large cities in the UK from the 1920s to the 1980s. A large proportion (c. 70% to 80%) of telephone traffic in ...
s 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, typically two letters plus zero, one or two figures (e.g. DA, EP5, LK85) followed by the number of the other subscriber on the fringe non-director exchange. To avoid confusion, three-letter dialling codes were not used for calls from the director area to the fringe area, even if they corresponded to the same holes in the dial (e.g. the Hoddesdon and Mogador codes were HO3 and MO4 respectively). 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 often given numerical codes to dial, and told to follow the code with the numerical portion of the other subscriber's number: these direct routings permitted the use of short unamplified lines. For director exchanges remote from the area boundary, the subscriber was told to dial a code (typically 7, 87 or exceptionally 1), to wait for a second dialling tone, and to follow this with the three letters and four figures of the other number. These calls were handled by tandem exchange ''Toll B'', from which the second dialling tone originated. To have a second dialling tone in this way was very unusual on the
PSTN The public switched telephone network (PSTN) is the aggregate of the world's telephone networks that are operated by national, regional, or local telephony operators. It provides infrastructure and services for public telephony. The PSTN consists ...
in the UK, although the French and Belgian PTTs had a similar instruction for when their customers made international calls. The distinction between ''trunk'' and ''toll'' became irrelevant when
subscriber trunk dialling Subscriber trunk dialling (STD), also known as subscriber toll dialing, is a telephone numbering plan feature and telecommunications technology in the United Kingdom and various Commonwealth countries for the dialling of trunk calls by telephon ...
was introduced. In North America, local telephone calls were typically unmetered and included in
flat rate A flat fee, also referred to as a flat rate or a linear rate refers to a pricing structure that charges a single fixed fee for a service, regardless of usage. Less commonly, the term may refer to a rate that does not vary with usage or time of u ...
billing. The term toll calling was adopted for long-distance calls which were subject to toll charges.


References

{{Reflist Telephony