I have a locked Cingular Treo 650. Mine pairs with my 2005 X5 flawlessly. I can even voice dial through the X5 system.

No you will not be able to access your phonebook but you can still do that through your Treo anyway. It will only load your favorites (quick dial numbers). Caution: make sure none of your quick dial numbers in your favorites have extra characters or this will cause resets in your Treo while pairing with the X.

If you receive or do a lot of calls while in your car, this is an incredible feature.