A telephone exchange equipment system for enabling transmission of a speech message from a fresh calling party to another busy party without interruption of the connection for the original conversation. Each of the telephone sets are connected to the exchange equipment through a four-wire cable comprising a transmitting line and a receiving line. The exchange equipment is provided with a mixer having two input terminals and an output terminal. During a time period when a first telephone set communicates with a second telephone set, when the exchange equipment receives a first telephone selection signal and a predetermined connection requirement signal from a third telephone set, the exchange equipment connects the transmitting lines of the second and third telephone sets to the two input terminals of the mixer while connecting the receiving line of the first telephone set to the output terminal of the mixer and maintaining the connection between the transmitting line of the first telephone set and the receiving line of the second telephone set.