I think I am going to try and sell my mini 3 and get an Air 2 from Staples. Right now they are really good prices and want to take advantage of it. I have a 64GB cellular mini 3. I set it up with T-Mobile (since AT&T locks the sim). My question is, what do I need to do so that it will revert back to having the choice to use any carrier? Just factory reset it? Or get another Apple Sim from the Apple Store? I appreciate any help.