Really quick question... Looking at a used iPad Mini 3. I know it's a universally panned device, but for the price ($200 for 64 GB w/ Cellular) I think it'll work well for what I need. The device is currently being used with an AT&T SIM. It's paid off, but it's been a while since I've bought a non-factory unlocked device... I can just pop in my Apple SIM w/ T-Mobile and take off, right? Are there different carrier variations of the Mini 3? Thanks!!