https://bugs.maemo.org/show_bug.cgi?id=8206

This is a bug I created some time ago about this issue, please go ahead and vote for it, maybe it will get implemented. It would definitely be a nice feature - I have a nice car stand for my N900, but answering a phone call is a pain since the speaker is not loud enough (due to the car noise). Being able to hear the phone call over FM would solve this nicely - no bluetooth sets needed.