I have a samsung galaxy s3.. sgh i747. android 4.1.2 version.. baseband version i747ucdmg2...kernel 3.0.31.1300972...network unknown...mobile network type unknown... use to be with att. trying to set up internet.. bought new att sim card.. wont work... it shows 2 bars for about 30 seconds, then nothing.. when using wifi, everything works fine....can get on internet, use phone, etc... att told me that its possible that the sim holder is bad...it use to work with previous owner.. I saw it...LOL...can anyone help with this??