Unlock T-mobile SGS3 for ATT network

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http://forum.xda-developers.com – Hello all, Long story short I'm trading my Galaxy Nexus for a T-Mobile SGS3 and I want to know if the phone can be unlocked and function on the att network, data and all. I've seen some discussion about the unlocking process and it involves unlock code websites that seem sketchy. I've also seen some talk of T-Mobile giving out the codes, but I'm not sure how I would go about that given I have no affiliation with T-Mobile. Are there any methods for unlocking on the forums that I am missing. I would really appreciate some direction, because there doesn't seem to be one preferred direction or (HowTos)