When two or more people with paired phones are in the car at the same time, the Bluetooth system should recognize all of them (or at least 2) and connect. The driver’s profile could be used to select the preferred phone for outgoing calls. But if the system is idle, any incoming call should be answerable from the car console, using the car’s speakers and mic.
There are multiple vendors that already provide the ability to pair and connect more than one Bluetooth phone at a time such as BMW, Lexus, etc.
For people with iPODs or portable DVD players being able to play over bluetooth while still being able to have the phone on bluetooth for incoming calls would be invaluable. I have to play Audible books on my iPOD over a tiny portable bluetooth speaker, which makes my friends all laugh - "tell me again, you paid HOW much for that car??"