Hey guys, Occassionally I'll see some iphones at pawn shops for sale. I currently have a non-jailbroken and non-unlocked 3G and would love to upgrade to the 3GS until the new iphone gets here this summer. My question is... is there any way to tell the difference physically between a 3G and 3GS? Sometimes, the iphones don't have any battery juice left so I can't tell. Also, say I did find a 3GS and bought it. Couldn't I just put my SIM from my 3G to a new 3GS and it work instantly, or is the SIM somehow tied to the iphone? And yes, I do pay AT&T for data. Thanks for the input.