Using Iphone from US in Thailand?

I have an exchange student currently living with me in the US from Thailand. She wants to buy the Iphone 5c because it's about half the cost as it is in Thailand. However she wants to know if she can use it back in Thailand. If she buys an unlocked version, can she use a foreign carriers? I was reading on an article that read "With the unlocked version, you can choose one that ships with a T-Mobile SIM card, or one without a SIM card at all. Both unlocked options work only with GSM networks." Can anyone clarify what a GSM network is, and if it means she can't use it there?

A sim card is a small chip that att uses in it's phones - it's your phone number. A phone requiring a sim card will not work unless an active sim is inserted. If you get an unlocked phone, you may be able to use it outside the US. A GSM network is the older cell towers - not 3g or 4g networks. I don't think the new iphones will work on a GSM network, as those towers are being phased out.

She needs to buy one unlocked iPhone 5S which she can use in Thailand. T-Mobile provides both locked and unlocked and you should get the SIM-free version which comes unlocked. She can use the phone in Thailand without any issue. If you need iPhone 5C / 5S unlocked or without contract cheaper than retail, mail me.

As long as it is unlocked she can use it back in Thailand with no problems. She just need to get a sims when she returns. I'm sure she knows where to get one here in Thailand. Now Thailand has recently got 3G service using 2100 mhz. Many people come here from the US and use their Iphone here. You can even get them unlocked here for about $10 at MBK Mall, 4th floor. Just for information the new Iphone5 16 mb is selling for 22, 000 baht while the 64 mb is 29, 000 baht.