Universal outgoing call restriction circuit

Abstract

A circuit which prevents a telephone or a plurality of telephones from making unauthorized or restricted calls to specific numbers or unspecific groups of numbers. The restricted call numbers may be local or toll call. The circuit is disabled either on a call by call basis, or indefinitely by entering a user defined pass code. The circuit is programmable from any commercially available touch-tone phone. When in the call restriction mode, the circuit detects outgoing calls by detecting and decoding standard `DTMF` burst. Upon detecting the first valid tone, the circuit isolates the user from the central office equipment. The circuit then parses the first and all following DTMF bursts and compares them against preprogrammed internal lists of fixed or relative restricted numbers. If a fixed number or a relative group of numbers is validly compared to the internal lists, the circuit continues to lock out the user until the central office will no longer accept a number, at which time, the circuit releases the line and restores the user to central office access. If no valid comparison is made to the internal lists, the circuit dials the remaining numbers in a burst mode, and restores user access to the central office as the call is completed. Use of the `*` key and `#` keys allow special programming options, and user disabling via special pass codes. The system may optionally be used with rotary dial phones and can be used with non-telephone voice and/or data communication systems.