I use one of these Hight-tech docking stations on the dash of my 1994 Jeep Wrangler. If for some reason it falls out of the "dock" or even out the door when I'm driving doorless, no worries. I have a nearly indestructible "dumb phone". I pipe the audio through the built-in phone speaker, avoiding the need for A2DP or even an AUX-in. No ground loops or interference from multiple bluetooth stacks.

Occasionally, I even hear a note or two over the road noise of a rusted-out 90's jeep built on 70's technology driven over unpaved roads. On the plus side, the roads are so terrible, I rarely drive more than 15mph, which keeps the noise minimal and the tunes-a-playin!