In my 2004 X5, you cannot have Bluetooth if you have BMW Assist unless you change out the TCU for an 2005+ unit. So if you want Bluetooth, the easiest way is to buy a Bluetooth module and replace your BMW Assist module with it. You will also need an eject box for the center console, and maybe a snap in adapter if you have the right cell phone for it. I spent way more than $300 for the conversion, so if your dealer can do it for $300, then it sounds good. But are you sure they are giving you Bluetooth, or just turning on the BMW Assist service?

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'06 X5 4.8is, TiAg/black, cold weather pkg., comfort seats
'07 750Li, TiAg/black, sport pkg.
'05 Ford F350 silver met./slate gray, Lariat, 6.0 PSD, CC, DRW, FX4