Samsung galaxy s3 can't connect to mobile network

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http://androidforums.com – Hi everyone, I am in need of emergency help here. I've been trying to solve this for about 6 hours now, I've spoken to tmobile, AND samsung and they couldn't give me a solution and I have searched probably the whole Internet.:mad: Okay so I had just gotten my s3 about two to three weeks ago, everything worked fine until about few hours ago I went to a classroom that has no service I tried using my phone unaware hat there was no service and it failed, so I put it away until class was over, afterwards I tried calling texting and using my data and none works I get the error no network connection (General)