i would just unlock with yellowsnow and buy a pay as u go sim over there, should work fine. iwould think, never been there but i wouldnt see why not, may not be able to use 3g but edge should work just fine. i would turn off data and just use as a phone
2G & 3G iphones work great in Thailand. Tried both DTAC and AIS. It must be jailbroken and activated 1st, then for the 3G you must install yellowsn0w. Then everything works 100%.
Note: DTAC pay-as-u-go data plan also works well in the big cities. But I would disable EDGE&3G when not using.