Abstract: Disclosed is an arrangement of circuits for providing what is normally called Custom Calling or Special Services features such as signalling and switching for a call waiting or three-way calling. The apparatus shown may provide either feature or may provide both services by the selection and insertion of one of three available circuits. A plurality of common circuits are provided to operate with specific electronic logic circuits for call waiting, three-way calling or both. Circuits are plug-in PC boards using integrated circuit logic. Individual plug-in cards are provided--one for the call waiting feature, another for three-way calling and a third card is used to provide both features. The entire apparatus may be connected to the subscriber lines and to the central office equipment at the main distributing frame thereby requiring no internal wiring or circuit changes in the central office.