3G/4G not working in Samsung galaxy S3 SGH-I747M My 3G and 4G is not working on SAMSUNG SGH-I747M. It's an AT&amp;T version of S3 so according to specifications it must support both. Can anyone tell what should I modify in order to get it working?
Check if your settings are correct. 

Go to Settings &rarr; More networks &rarr; Mobile network &rarr; Network mode and select as the image below is selected. If this doesn't work it may be the signal strength in your area 

(Click image to enlarge)