I have searched b4 posting regarding that issue but didnt find anything related to the n900. anyway i have a car kit installed that i imperatively rely on for my work. I connected the set to my n900, all went good, the devices gets paired and the n900 shows the headset icon... only that the audio seems unavailable... i make a call and cant hear anything... any clue on how to fix this?
thanks

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.

Not sure if this helps but worth a go. I had choppy audio for the person on the other end of the call. once I start a call (can be ringing) then I use the 'Headset' button to disconnect audio whilst leaving bluetooth connection active. A second press redirects audio to the 'Headset' and seems to resolve the issue. Let people know if this helps.