I purchased a new 64GB WiFi+Cellular iPad Mini directly from Apple UK. I am now spending a couple of weeks in the US. I go back and forth fairly frequently. With my iPad (3rd Gen), also purchased from the UK Apple Store, I pop in an AT&T SIM, buy 3GB of data, and happily use the iPad on AT&T's cellular network while in the US. I have just tried doing the same thing with my new iPad Mini. Stopped into an AT&T store, got a nano-SIM, popped it in, and -- "This device is not supported". I went online to ATT's SIM registration page, put in the IMEI number, and... based on the IMEI number of the iPad Mini, this device is not supported. I spent some time talking with AT&T tech support, and they don't know what to do because their internal systems say the IMEI is not supported. I have spoken with Apple tech support, and they don't believe there should be any problem, but it's up to the carriers to offer support... Now, I don't expect LTE to work. I would, however, expect 3G & maybe 4G HSDPA/HSDPA+ to work. But maybe not. Is the cellular hardware in the new Mini so very very different? I have just now had an AT&T supervisor tell me definitively he does not expect an iPad Mini bought in the UK to work on their network. UPDATE Friday the 21st of December: I walked into a T-Mobile shop and asked for a nano-SIM for the iPad Mini. The nice lady said, "Sure! You want pay-as-you-go?" We popped in a SIM, I subscribed to the (minimum) 5GB for $50, and it works! About 9Mbps down, 800kbps up on '3G'. So an iPad Mini, purchased in the UK, is supported nicely by T-Mobile in the US. But not AT&T.