You have DSP right? This was discussed at length on the ....E39.....bimmer.....forum....thread. Since the DSP system actually controls the volume the dynavin cant level the call volume like it would in a non-DSP application.....what you need to do is lower all the source volumes in the settings menu and make sure the volume on your phone is all the way up.

Also lots on changes with the way volume is handled in the newer firmware, make sure you read up about it on the other thread....or at least make sure you understand the DSP specific instructions that are with the firmware download.