No dice with Nokia N900 here as well. When it comes to the N900 devices the problem is that the Bluetooth deamon (bluesz) does not have the PBAP profile compiled in it. Also, another complication comes from the fact that the N900 will aggregate various information about your contact like IM accounts, physical addresses, etc etc. When you try to send that information to your BMW, it is dumping everything and this confuses the car BT module.
In the case of the N900, some people have had limited success by following this process:
1. Install the Petrovich app from maemo.org
2. Go to Contacts -> Export
3. Follow the wizard. At some point it will ask you to choose VCARD format. Choose version 2.1 not 3.0
4. When all of your contacts are exported, they will be somewhere on your filesystem.
5. Find the actual vcard files and use Petrovich to send them to Bluetooth.
Again, this is limited functionality and it works only if you just have Name and phone number in your contact details....