Abstract: A key telephone system, having ports for connection to telephone lines of a telephone exchange and ports for connection of terminal apparatus including key telephone sets, is provided with the ability to distinguish if an intended call or feature access involves more than the key telephone system. If so, a signalling protocol of the telephone exchange is emulated on behalf of the terminal apparatus and transmitted via one of the telephone lines whereby the progress of the call or feature access continues, as if a user of the terminal apparatus had initiated the signalling protocol of the telephone exchange.