A car telephone system having a telephone module (3) which has a telephone transmitting and receiving unit (5), can be connected to a transmitting and receiving antenna (7), can be connected to a central control bus (1) of the vehicle and can be controlled by a central controller (2) via the control bus (1) enables telephone operation, via the telephone module (3), using user-specific data from a mobile telephone (9) by virtue of the fact that the telephone transmitting and receiving unit (5) is provided with a wireless data and signal transmission unit (6) which can be used to transmit user-specific data from a mobile telephone (9) to the telephone transmitting and receiving unit (5), and by virtue of the fact that the telephone transmitting and receiving unit (5) is also connected to a separate card reader (11) for a memory card which contains the user-specific data from the mobile telephone (9).