This question is raised a lot and having just visited the US from the UK and successfully activating an AT&T sim I can confirm it can be done. First step go to an AT&T store and buy an iPad simcard. Apple will not sell them and unlike here in the UK the simcards are not free cost me $16. Then you need to have a US registered visa card and address to activate it. If you have friends relatives who can help with this then great, if not then go buy a Visa pre loaded gift card and put enough money to cover the monthly subscription on it, I got mine from Best Buy. Then I put the sim card in my iPad went to the settings, the simcard was recognized by the iPad and allows you to register it (even though it was a UK model) use your hotel address and zip and enter the visa card details. At the end of your trip remember to cancel the recurring payment so that you can reinstate it in the future or the sim card may be blocked.