A mobile telecommunications system has a handset and a headset for connection to the handset. The handset includes an RF transceiver for transmitting an outgoing call and receiving an incoming call, and a processor coupled to the RF transceiver that provides audio signals on a first audio path to an audio transducer in the handset and on a second audio path for an audio transducer in the headsets. The headset and handset include respective button switches arranged that the operation has the effect both of initiating and/or accepting a call, and of routing audio signals to the respective first or second audio paths. Embodiments are described including a separate switch for toggling the audio paths, and automatic sensors for detecting use of the headset or handset.