Abstract: An automated prefix dialing system is disclosed to allow a subscriber/user to automatically insert a predetermined prefix dialing code in certain outgoing telephone call situations. The system is electrically disposed between the telephone company's central office circuit and the subscriber's circuit. The system preferably comprises six sub-circuits: DC power path circuit (off-hook sensor circuit), shadow-ring detector circuit, isolation circuit, DTMF receiver circuit, DTMF generator circuit, and micro controller circuit. When not in use, no power is used by the system. The DC power path circuit, provides power received from the central office line to the various circuits and components of the system when the subscriber's phone is taken off-hook. Off-hook sensor circuitry detects when the telephone has been lifted either in response to an incoming call or to initiate an outgoing call.