Thanks for all the info sna77!
Initially I had thought it would be more cost effective to get a new aftermarket stereo with BT built-in. But the phone book, steering wheel integration, and possible voice recognition compromises are making this a bit more thought provoking. So, to be clear, the TCU install will allow these mentioned features even if the 2006 X3 does NOT have nav, assist, etc. The vehicle does have the Business CD and I've been led to believe that the necessary wiring is in place 'cause there is a small bundle of non-landed cables/connectors in the rear left side compartment. The steering wheel has the RT button also.
I'm guessing that I would also need the mic and, again, this vehicle should have the pre-wiring.
So aside from the TCU and microphone, is there anything else to be considered for this upgrade?? I realize that the phone needs to be placed somewhere but I want to cost out the minimum hardware needed for functionality first.