OK sorry I'm late to the party, but I am still using the original 2G Iphone and want to upgrade. Problem is, I don't want to upgrade through AT&T and was planning on purchasing an iPhone 3GS from ebay and using that. I've read through some threads on here that say that I WILL be able to use my 2G SIM card in the used 3GS I purchase, but I had a few questions. Most notably, do I need to purchase an "unlocked" phone off ebay, or will any 3GS work? Most of the auctions I see are for used 3GS's, and I assume I can just put my sim card into this phone and it will work correctly. Is this an accurate assumption? Will I have to activate the phone at all to get it to work, or can I just power it on, put my SIM card in, and it'll work just like my 2G does now? Thanks a ton for any info.