X3 bluetooth kit, a-la-cart style on E-bay
 

Purchased an almost complete (missing screws / bolts) 84 64 0 306 854 "RESTORIFT KIT HANDS-FREEE FACIL. BLUETOOTH" from Germany.
It's posted on E-bay with options for the ULF ($295) and complete vehicle wiring harness ($125, though USA spec X3 shouldn't need the wiring).

I planned to cannabalize it for my E39, but ended up getting my parts from E-bay & dealer, and no longer need it.

Search for E-bay item: 5860618929

Thanks to all the previous forum posts which helped me get bluetooth into my "ancient" 1999 E39!