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 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 was introduced. In North America, local telephone calls were typically unmetered and included in flat rate billing. The term toll calling was adopted for long-distance calls which were subject to toll charges. References Telephony