61 00 ... External jump-starting aid and car telephone!
WARNING: This page is about a different car, the 2002 BMW Z3 and 2001 BMW Z3. However, it is still accessible from the selected car via links, so may be relevant.
Siemens C 2:
When starting engine with assistance of another vehicle, remember that overvoltage could damage the Siemens C 2 telephone. For this reason, always disconnect the sender and receiver from the electric system before using outside starting aids.
Siemens C 3 And Motorola C 451:
Sensors and receivers of Siemens C 3 and Motorola C 451 telephones are protected against overvoltage, but calls may not be made or received during external starting procedures.
Always pay attention to the operating instructions of different type and different make telephones. In case of doubt, disconnect sensor and receiver from vehicle electrical system.