I purchased a "new" unlocked Samsung Galaxy S4 Active SGH-I537 phone on E-Bay. Everything works fine except when I use the phone with my local carrier SIM card. When I insert the SIM card and turn on my phone, the carrier name appears and I get full bars. I can make a call or two, but then the carrier name is gone and no bars. At times I get the message: "Mobile network not available". I can’t make any more calls and if I try to the whole phone freezes and I have to do a hard reset.
When I first turn it on and don't try to use the phone app, I can go into Mobile Network and see the list of my local carrier in Network operators. If I try again to go into Mobile Networks, the network bars go to zero and get the message "Insert SIM card to access network services."
I’ve tested the SIM card on my old phone and it works perfectly. I have checked and the frequencies are the same for my local carrier and AT&T's.
I would appreciate any help on this matter. Thanks.