I successfully unlocked a [WEEK37] iPhone 3GS for my Dad; he frequently travels overseas. Everything appears to have worked in the US but he recently went to Thailand and could not get service with the SIM he used. Is this a problem he's going to run into frequently? I suspect I should have turned-off 3G then unlocked as you are supposed to do on T-Mobile. His phone works in the US on AT&T. Thanks all!