I have the V600, V551 and V3 Razr and all work flawlessly with the BMW Bluetooth system.
Look at the various links on this page under the V710 and you will see the host of issues that most people have with this phone. Very few have been satisfied with it.
http://www.xoutpost.com/file-bmw_bt_phones.htm When it gets to the point where people band together and file a class action lawsuit, that spells trouble in my book.
The e815, from the reports I've read, seems to be a better Bluetooth phone.