I recently got a Q7 and really like the integrated bluetooth. Can I install an OEM B7 headunit with bluetooth into my '03 A4 and have the bluetooth work? Does the B6 have the microphones? Was thinking of adding a DICE unit at the same time.

The phone interface (a.k.a. bluetooth) is always an external device connected to the head unit. If you install a B7 head unit and a B7 phone interface then yes, it will work in your B6. And no, you need the complete harness, BT antenna, microphone and the phone interface besides the head unit. If the head unit is not the RNS-E navigation plus you should also have a multifunction steering wheel.

Sounds like it's definitely not worth the trouble.