i wouldn't trust any of those auctions. no one has been able to unlock the iphone yet (the closest i've heard about is sim-modification that makes the iphone think the sim in it is an at&t one when it's not). keep an eye out on the news here or at hackintosh to see if/when the iphone is really and truly unlocked to allow any gsm sim card...
what auctions are you looking at?
this one is deceptive - they say it's unlocked, but then say later that you can't use the phone/data/text/email but you can use the ipod and other functions that need data via wifi. somehow that means unlocked to them

but don't be fooled by those...