Sure.....I did it. Want to read the thread about it??
From 3 years ago: Clicky Here
Since this link is not working for me, I thought I'd let all know - yes you can put a OEM head unit from a '09 G6 into a '06.
My original unit is P/N 15777349. It is a 6-CD changer with the P-TYPE, MSG, CLOCK, EJECT on the right and INFO,MENU, ENTER, LOAD on the left. Bottom has RPT, SONG LIST, and RDM.
I bought a P/N 25890720 from LKQ thru Ebay. They did not claim this radio would work in anything other than the '09 it was removed from, but I saw other eBay sales that claimed this part would work so I took a chance.
This radio is a virtually identical 6 CD changer, but it has the front AUX jack.
As soon as I connected it, the messages (Oil Life and so on) worked.
$80 at the dealer got it unlocked and now everything works...including the aux input.