Call screening in a public telephone station

Abstract From the Canadian patent

Abstract, Control equipment employed in a customer-owned public telephone station prevents a user from making unauthorized telephone calls in a telephone system. Operating under the control of a computer in the station the control, equipment employs a call screening process which restricts the telephone numbers a user can dial to those numbers preselected by a station owner. The telephone numbers are categorized in multiple but distinct groups each of, which represents a specific class of telephone call. The control equipment is responsive to momentary loop breaks occurring on tip and ring lines connecting the station to a central office, and to a loop break provided by the central office …