Bangkok Sim Card for data roaming

[inquisitor]

Check out this post, according to which your Nexus S would work on AIS and on TOT3G.
By the way Huawei has recently released the first pentaband 3G handset running Android, the Ascend P1, which virtually supports all the global 3G frequencies used today (850, 900, 1700/2100, 1900, 2100). It only lacks some Japanese frequencies (700 and 1700), which are of minor relevance.