To answer an earlier question, the 639 kit should work for all I-Bus based vehicles (X3, X5, E38, E39, Z4, E46). That kit was paired w/ an aftermarket camera on an E38 in the write-up on bimmerboard.

If now you're considering going full OEM, just get the current kit that mgruber mentions: 66 21 0 397 648
It has the switchbox w/ multiple video inputs and the handle strip w/ integrated camera. Ask your BMW parts dept for the instructions from ASAP (AfterSales Assistance Portal). No reason they can't order it - is a US spec kit w/ the cheesy US warning label they want you to stick to your nav screen!

__________________
2010 X5 3.5d: SOLD, but miss the torque...
2004 X5 4.4i: SOLD, but served us well