Abstract: A motor vehicle built-in unit for a mobile phone has a central control unit and an interface for exchanging signals between the central control unit of the mobile phone and the motor vehicle. The built-in unit also has a motor vehicle-specific adapter control unit for adapting functions of the interface and/or of the central control unit to the respective type of motor vehicle. The modular design allows for electrical and mechanical adaptation to various types of motor vehicles so that the central control unit and interface can be identical for a wide variety of motor vehicles. An alternative built-in unit has a central unit and an interface for connecting to the motor vehicle. The interface is designed to connect the built-in unit to the motor vehicle selectively either with a standardized plug-type connector or a motor vehicle-specific plug-type connector. The motor vehicle built-in unit can therefore easily be adapted to the type of plug which is used in the respective motor vehicle.