GM did you a favor. I have a Kia with the Microsoft system. An Apple iPhone can crash the system so hard that it needs a full reboot. You have to stop the car, turn the engine-off and restart to get the phone interface working again. The system doesn't work with Android properly either. I assume Microsoft's system must work well with a Zune or a Lumia phone, however I have never seen one to try it out.
Keep the engine stuff separate than the entertainment stuff. If you let Microsoft near your car controls, then it will be like the old Bill Gates compares Windows to a GM car joke.