Same problem when trying to use my Droid X in my car with the built-in factory bluetooth ('07 Camry, JBL System). Alerts and rings continue to sound through the phone itself (and through the car speakers, but with a different ring).
Also, audio pairing is intermittent. I can hear them, but they often can't hear me. Mic audio comes and goes.
Not surprisingly, Verizon & Motorola both say it's Toyota's fault. And Toyota says it's the phone's fault. Hmmm...
All our other family cellphones work just fine in this car. (several Blackberries, LG, etc.)
Come on, Motorola, get your act together. And Verizon, you bill the Droid X as your flagship smartphone?