[1] 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.
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.
To have a second dialling tone in this way was very unusual on the PSTN in the UK, although the French and Belgian PTTs had a similar instruction for when their customers made international calls.