From a quick search, it looks like Thailand uses GSM (AT&T/TMobile) and not CDMA (Verizon/Sprint). So you will not be able to use your phone unless it supports

From a quick search, it looks like Thailand uses GSM (AT&T/TMobile) and not CDMA (Verizon/Sprint). So you will not be able to use your phone unless it supports both bands. https://discussions.apple.com/message/18588063#18588063 https://discussions.apple.com/message/18588063#18588063