As an update - since my last post back in October I picked up a cheap bluetooth car stereo (Tevion from Aldi) at Christmas.

A2DP works great, and the track up/down and play/pause on the stereo control the N900 media player - absolutely ace, and well worth 40 quid. It doesn't pick up the contacts and recent numbers from the phone, but that ain't no loss. Picked up a car holder from ebay which the N900 just clicks into instead of a universal one.

Also just fitted a full Zagg invisible shield kit as I found them for a tenner on www.play.com - much better than the proporta crap I bought when I got the phone.