[VegasMike]

The built in phone functionality with On Star is based around their prepaid cell service and there is no way to adapt a personal phone to it. You would have to purchase minutes from them and use the cell number they issue for your On Star service.

Connecting a cell phone to the stock radio really only became possible over the past few years as manufacturers finally added that function to stock radios. Obviously Hummer disappeared well before that factory option was available.

Basically to add the functionality you want, you're going to have to replace the factory stereo with an aftermarket one which will allow you to use On Star and your cell phone. You can look into one of those parrot devices that gives you hands free use, but not the full integration that it sounds like you are after.

Replacing the stock radio is actually quite easy, and with the correct parts you can maintain On Star, door and warning chimes, and even the steering wheel controls. There is another thread in this forum that describes what you'll need.