I had a similar problem. I have a Jawbone headset and it generally works just fine. Last week I rented a Prius and when I tried to use the headset there was no audio, neither in the headset or the phone.

When I shut off the headset the phone worked just fine.

I restarted the headset outside the card and it was OK. The next time I got into the car, it was dead again.

I attributed it to BT confusion with the car radio.