A circuit arrangement for a mobile communications unit of a motor vehicle, having a first mobile communications module for a mobile communications transmission according to a first mobile communications standard, a second mobile communications module for a mobile communications transmission according to a second mobile communications standard and a reading unit for reading identification data from a chip card. For a reliable mobile communications connection, both for telephony and for the transmission of other digital data using control devices and personal computers, the circuit arrangement is configured to operate the two mobile communications modules simultaneously, and the reading unit is configured for the simultaneous operation of the two mobile communications modules to receive identification data from two subscriber identification modules from the same chip card and to transmit the identification data of a respective subscriber identification module to one of the two mobile communications modules.