[ctuna]

I can't see any reason to replace a TCU
Especially if you don't already have one.
(Go aftermarket for those funcntions)

You can get used Mulf 2's that have a USB option
for 200 bucks on ebay . There also aftermarket devices
like a Dension Gateway 500s bluetooth that will give you
bluetooth phone and music plus usb ipod that have a lot
more functions than the TCU.
All of the above will require some programming that the
dealer won't do however.
The dension programming is pretty simple.

Or if you have the pro radio you might consider a dynavin N6.
If you have idrive you could to a combox or NBT upgrade.(not sure of the details on that)