Thx for replying.
Disabling the carphone is of course an option, but
I've an BMW with an integrated phone en audio system with an adapter for the iPhone as a music carrier. So the music on the iPhone can played on the carsystem and also the TomTom instruction can be heard over the speakers. So, disabling the carphone forces me to get a bluetooth kind of system for the iPhone. That is last resort but possible indeed.