Not many people are aware of this but att actually provides unlock sim codes up to 5 a year. I believe you just have to be in good standing with them for like 3 months or something close to that. Just call them up, they'll either do it over the phone or direct you to a website to submitt a request. I called them up recently to get the sim unlock for my gs4. After a few minutes they gave me the code. Now as soon as I get my note 3, I can sell my s4 as an unlock.
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