2006 Cadillac Escalade (no bluetooth) and Iphone help?

So I own this 2006 Cadillac Escalade and I have an active XM Radio account, it also has Onstar which I don't subscribe to and it doesn't seem to have bluetooth anyways. I just wanted to find out if there is a way of using my Iphone through the trucks system so I don't need use my ugly, annoying handsfree device that I have clipped on my visor. If you can help give me instructions on how to connect my Iphone through my satellite radio and/or Onstar that would be greatly appreciated! : ) Would I need to purchase any devices because I'd prefer just to use the Cadillac manufacturers microphone/speaker system built into the truck as it's very nice and clear! Seems pointless to have options available that I cannot use : ( I would be using my cellphone account which also has full internet service as well if this helps at all... Thanks! : )