Hi Norbert, have you tried deleting any existing HFP pairings from your car first? I recalled seeing a post on the Android project forums about this when using a Samsung Galaxy. (http://code.google.com/p/android/issues/detail?id=4402
"Samsung Galaxy S 2.1 works fine in my 2009 Audi Avant (RNS-E type system) and 2010 Porsche Carrera (full PCM) in rSAP mode. As I've seen a few questions about this.. note that (1)Only contacts on the SIM will be uploaded to car system (this isn't an unusual restriction, my old HTC touch HD did exactly the same)and 2) that on the Porsche PCM for some weird reason you need the dealer to hard-code the PCM TO rSAP mode, or it only does HFP.
When you're pairing on either system delete any HFP pairings for the same mobiles and start the connection from the car head-end system the first time and be quick entering the 16 digit rSAP pairing code as they both time-out pretty quickly.
Now..before I update my Galaxy S to Froyo..anyone know if rSAP on that works? LIke many others I suspect I'd rather have the incredibly useful rSAP than Froo I think!"