I retrofitted the BMW Bluetooth system into my 2001 X5 and it was very straightforward. I am able to pair lots of BT enabled phones, including but not limimted to the Motorola V600, Motorola V551, Motorola V3 Razr, and the SE Z600. See
http://www.xoutpost.com/articles.php?...ticle&artid=26 for my installation.
My vehicle has the phone prep, but it sounds like yours may not. According to Jan's write-up at
http://www.janixworld.com/x5/phone/ the kit you need to buy if your car does NOT have option S640A installed is part number 84 64 0 153 227 at approximately 750 Euros (without snap-in holder,plus tax) and installation time is somewhere around 10 hrs.