I believe this is a software issue. With the latest up-date to my recently previous Droid X, the problem began and now continues with my Razr Maxx.
When my phone is paired with my VW's Bluetooth phone system and I then use the Google Navigation function in the car, the guided map routing works, but there is no voice turn by turn functionality. The navigation voice works OK when I turn the pairing off but then I can not use the car's hands free phone system.
I hope that the pending Ice Cream Sandwich upgrade will take care of this issue - when it ever arrives. Galaxy Nexus just released an upgrade (4.0.4) to ICS and the Droids are still waiting for an initial 4.0...really?