Alright I'm trying to help a friend out whose looking to switch to t-mobile. I suggested he purchase a factory unlocked iPhone 4S instead of buying a jailbroken iPhone 4 that is unlocked using ultrasnow or a gevey sim. Well, I've been searching around and noticed individuals that are buying used at&t iPhone 4/4S and buying At&t sanctioned unlocks from websites or other forum members on marketplace forum. Can anyone enlighten me on exactly how this process works and any important notes I should know when buying a used iPhone 4/4S. I've been hearing that if you buy an iPhone 4/4S thats attached to an at&t contact the unlock won't work, is this true? Only reason I ask is that going through the at&t route seems to be considerably cheaper than purchasing a factory unlocked iPhone.