I just bought a galaxy s4 mini GT-i9192. I have tried a bunch of different apn's and I'm not getting anywhere. I have a t-mobile sim card from straight talk, is that the right one or do I need the at&t sim card? what is the correct apn? I have no problem making phone calls and texts but, the service is only G. In the same areas I used to get 3G no problem with my old phone. Thanks in advance for your help.