[Cooper197]

So if it were me, I wouldn't change the head unit.
Instead, I'd buy 2 integration kits.

CoStar has an excellent bluetooth unit (BlueStar) that replaces the factory onStar system using those buttons, the factory microphone and factory speakers. Also will lower the speed of the A/C blower motor if it's on high for the duration of the phonecall and does all sorts of cool factory integration things. (Have one for my 2005 SRX, love it)

Then, using a kit such as an iSimple IS77, or a factory integration for a Denali/Tahoe/Suburban/Silverado/Yukon/Sierra/Escalade for the Aux port or iPod adapter.

Replacing the head units in these cars, even if done yourself, is nearly $1,000 for a quality head unit and all of the expansion modules you'll need to keep the car doing everything it's supposed to.
Just getting integration kits such as I have mentioned is much cheaper, not to mention it keeps the factory look giving thieves less of a reason to look at your rig.