Ive successfully unlocked my HTC Imagio and am now using it on T-Mobile. The Sim must be unlocked first and then go under phone and then options and change the settings to GSM/UTMI only. You will only get egde service which im told is middle range but I think its slower. Im having a problem with the data though because you are supposed to setup an APN suing T-Mobiles settings but I am missing a screen, so I am told directly from HTC, even after flashing rom after rom after rom to find out why I am missing this and I've searched through every forum and database to figure this out with no success so Im stuck with WIFI whenever I can get it. I know it is possible to setup because others have on ATT and T-Mobile.