Yeah, for a while now I have been having this problem with my droid (even since 2.0) where I would be using my droid as a music player in my car and afterward, would need to place a call to someone. For some strange reason the earpiece audio is completely OFF, but the call still goes through. I haven't tested to see if voice is transmitted, but you certainly cannot hear anything (not even a ring).
Anyone else having these issues? I had to restart my phone for it to work again.