I have a factory unlocked iPhone 4s for use with GSM sim cards here in Thailand. I'll be making a short trip to the US soon, and I'm wondering if there is a cheap and easy way to have use of my phone while I'm there using a pre-paid US GSM sim card. I figure as long as I have an unlocked phone, I may as well take advantage of that if it doesn't cost me an arm/leg. I would be looking to have use of all the iPhone functions, and avoid having to change any settings on the phone to accommodate the US sim, as that kind of stuff confuses the hell outta me! Especially when I'd have to change them back again. So I'm essentially looking for a situation where I can just pop out my Thai sim, and pop in a US sim, and be good to go. Then pop out the US sim and go back to my Thai sim when I return. Ideally, having a US sim card I can keep active for a longer time, and switch from my Thai sim for any time I'm in the States, would be great. But as I only travel there appx once a year, I don't know if that's feasible money-wise. And I don't want to enter into any long-term contracts. Any help with providers and approximate costs would be appreciated also. Thanks for any information.