Galaxy S3 not getting 3G on Straight Talk

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http://forum.xda-developers.com – I recently bought an international unlocked S3 from Amazon and popped a Straight Talk micro sim into it. Unfortunately, I am only getting EDGE. I've tried all sorts of APN settings but to no avail. Is there a setting I'm missing or anything I can do to get 3G on this phone? Thanks. :) (HowTos)