12 00... External jump-starting aid and car telephone!
WARNING: This page is about a different car, the 2002 BMW M Roadster, 2002 BMW M Coupe, 2001 BMW M Roadster, and 2001 BMW M Coupe. However, it is still accessible from the selected car via links, so may be relevant.
Siemens C 2:
When starting the vehicle engine with outside help from 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:
Senders and receivers of Siemens C 3 and Motorola C 451 telephones are protected against overvoltage, but calls may not be made or received during outside starting.
Always pay attention to the operating instructions of different type and different make telephones. In case of doubt disconnect the sender and receiver from the vehicle electric system.