I just got a brand new replacement iPhone 4 and am considering selling it and getting a new 4s. In order to help me make that decision, I'd appreciate folks input on the following questions: 1) What are some reasons why people buy an unlocked iPhone? Are the data plans really cheaper when not under a contract? If so, why doesn't everybody switch to one of those cheaper data plans after their contract runs out? 2) Will I be able to sell my phone as unlocked? I bought it when the iPhone 4 originally came out, so that's less than 2 years ago. However I know that I am upgrade eligible. If I upgrade, will my old iPhone (that is now a brand new iPhone 4) will become unlocked automatically? 3) Can I change provider in this move, or does it require that I stay with ATT? My understanding is that my contract really only ends 2 years after I got the phone, unless I stay with ATT and upgrade.