An adjunct Type II caller ID/call waiting (CIDCW) receiver unit is provided which has a greatly improved ability to detect tones and other call related information on a telephone line from a central office while the customer premises equipment is in an off-hook condition. The inventive adjunct CIDCW receiver unit is placed in series between the telephone line from the central office and the customer premises equipment, rather than in parallel with the customer premises equipment as in conventional adjunct CIDCW receiver units. A second telephone line interface (TLI) is included in the adjunct CIDCW receiver unit for connection to the customer premises unit to simulate the impedance of the telephone line. The adjunct CIDCW receiver unit has the ability to disconnect, mute or suppress the microphone signal from the customer premises equipment from being included in the signal received by the call related information receiver portion of the adjunct CIDCW receiver unit.