A switching device for connection to an antenna unit and a computing unit to form a communication device for car-to-X communication, in particular a DSRC communication device. The switching device has at least one interface for communication with a mobile terminal device, in particular a mobile telephone. The switching device includes a computing unit and a control device to forward at least a part of received messages to the mobile terminal device and/or to transmit messages on the basis of a control command from the mobile terminal device.