Intercepted Number
In the middle 20th century in North America when a call could not be completed, for example because the phone number was not assigned, had been disconnected, or was experiencing technical difficulties, it went to an intercept operator who informed the caller. In the 1970s this service was converted to Automatic Intercept Systems which automatically chooses and presents an appropriate intercept message. Disconnected numbers are reassigned to new users after the rate of calls to them declines.
Outside of North America, operator intercept was rare, and in most cases calls to unassigned or disconnected numbers would result in a recorded message or number-unobtainable tone being returned to the caller.
Read more about this topic: Telephone Number
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—Voltaire [François Marie Arouet] (1694–1778)