Abstract: The invention provides a method and apparatus for the prevention of fraudulent toll calls by a user connected to a key telephone system. On recognition of a user request for use of a telephone line to make a call to a destination outside the key system, the forward speech path to the seized telephone line is muted. The string of digits dialed by the user are monitored and evaluated for correspondence to restrictions associated with the user terminal. If restrictions are failed, the call is terminated; otherwise, the forward speech path is unmuted and the call is allowed to proceed in the conventional manner. The invention may also provide an interdigital timer which is set upon reception of each dialed digit whereby if the timer is allowed to reset while the dialed digit string is being monitored, the call is terminated.