Treo users:
Do I need Treo^TM Voice Dialing by VoiceSignal loaded onto my Treo to be able to use the voice dialing feature in the A6?

I'm fairly certain that once the phone is bonded to the car via bluetooth, the only voice command that will work is that which is installed in the car. I know with my e815 that I can no longer use the phone's voice command interface once it's paired.

Safelder is correct. The voice command is disabled on the phone once the vehicle is bonded with the vehicle via bluetooth. Also the documentation for the cradle says the same thing, so even if you get the cradle for the Treo 650 you have the same issue.