I own an 09 w/ XM. My wife a '10 without. They are obviously the same radio, hers is even sattelite ready with onstar. After reading forums for more (ahem) popular cars, its also obvious that there exists an adapter that plugs into the back of the radio, as well as adapts to the wiring harness as well. These other aforementioned kits also usually come with a new attenae as apparently the onstar antennae may not be equipped to handle XM as is.

XM customer service is ignorant and clueless, and chevy customer support transfers me to XM.
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Any takers? I do not want to buy a 3rd party tuner. I want it through the stock radio, just as mine is.