[MrDK]

Two things you need to consider in your choice of cell phones is the band that it is capable of and whether it is locked of not.

There are two bands in the US and two other in most of the rest of the world. All phone you buy in the US can handle the two US bands, so if you buy one that is tri-band or quad-band it will include at least on that is compatible with the phone systems in Thailand.

Almost all phones sold in the US are locked to a carrier, such as AT&T and a non-AT&T card will not work, including those in Thailand. Unlocking a phone is not hard, especially in Thailand. It can be done for $10 or so.

My advise would be to either buy one there, perhaps used; or buy one on eBay. I bought a couple on eBay from UK and AUS sellers. Each cost me about $40. They are dual band, but designed for the non-US market so the cover both bands in Thailand.