Ok so the girl I'm dating has a sprint iPhone 4 that has the usual broken lock button and its just slow and the data is slow. I have bought and sold GSM iPhones before but never dealt with CDMA Sprint or Verizon iPhones. I have heard stuff about good and bad ESNs. Basically I need help understanding what I need to know to buy a good one to activate on Sprint's network. Now I don't mind a little effort to make it work if getting a bad ESN to work so I can get one at a cheaper price. Just need to know how I would do that. So help educate me!