I picked up a Griffin BlueTrip and it works flawlessly in the X5.
This was a replacement for a simple Aux-In input. There are better solutions out there but for $65 it's an improvement over fumbling around for a cord and trying to plug my phone into the arm rest.
1.) Paired with an iPhone 4
2.) The phone or car is smart enough to use the car's telephone bluetooth when a call comes in or I make a call going out.
3.) The power source in the center console turns off with the car
4.) The phone seamlessly pairs with the BlueTrip and the car.
Lastly, this is not iDrive controlled so if you spend a lot of time in the car listening to your ipod, this is not an optimal solution.
However, if you take a couple of roadtrips a year and don't want to fork over for an integrated solution, this is a step up from a plain Aux-in solution.