A handsfree car mounting kit for a mobile telephone (6) coupled to a head-set (4) via a Bluetooth radio module consists of a passive communications unit (1), which has a loudspeaker and a microphone (5), optionally coupled to an amplifier, arranged in a cabinet which has a bearing or a holder on its outer side in which the headset (4) may be placed and connected electrically to the communications unit. Further, the cabinet is provided with a plug terminal for a 12 volts socket terminal (3), such as a cigarette lighter in a car. The headset (4), which has a digital signal processor (7) containing inter alia a Bluetooth radio module an optionally a noise reducing circuit, is coupled to the bearing or the holder in the communications unit such that it can detect the voltage applied to the communications unit, and by means of a switching circuit (11) it is possible to adapt the digital signal processor of the headset and the control knobs of the headset to function with the loud-speaker (2) and the microphone (5) of the communications unit. Hereby, a handsfree car mounting kit of a simple structure is provided, just using a few and simple components, and all the vital parts from the headset (4) may be switched to cooperate with the loudspeaker (2) and the micro-phone (5) of the communications unit.