I recently got a iPhone 5s to replace my iPhone 4. I did a factory reset on the 4 with plans to sell it on Craigslist. As soon as I listed it i started getting emails asking if it was unlocked. After doing a bit of Googling, it looked like all I had to do was contact AT&T to get an unlock code. I received it today. It requires hooking it up via USB to my computer and connecting with iTunes. In order to do this I'm going to have to go through set up andinput my country, language, etc. first. My question is, once I unlock it, can I then do a factory reset and wipe it clean and have the unlock stay? I want to wipe it clean, but don't want to lose the unlock which seems so important for resale value.