Hi, I bought an unlocked ATT Galaxy S3 off of Craigslist. The owner was using it for T-mobile, I'm trying to use it for ATT. The phone makes calls, the wifi works, but if I try to use my data it will not work and says network error. I've tried resetting the device and that didn't work. Anyone have any ideas on how to get the network internet to work? Thank you, any help is greatly appreciated!