Abstract: A telephone set (1) has an analogue telephone port (2) for connection to an analogue telephone network, and a controller (13,21) for generating routing control signals at the telephone port compatible with the telephone network and being responsive to input signals to control operation of the telephone set. A power supply port (19) is connected to the controller (13,21) and to a power source. A serial interface (37) connects the controller to a processor (8), whereby the control means is responsive to input signals supplied via the serial interface (31,7) to control operation of the telephone set. The telephone network is isolated from each of the serial interface (31,7) and the power supply port (19) while permitting data transfer between the telephone network and the control means.