I bought a nexus 4 from a dude on craigslist so i don't know it it's from t-mobile or the play store. anyways, i used on H2O (at&t) for a month it worked perfectly. later i switched to Simple Mobile (t-mobile) it work great for a week than all the sudden i don't get signal. i put an at&t sim it works fine. i tried several different t-mobile sim, but i never got signal. my nexus only works on at&t now. i restored it, didn't help . i called google customer service, they did everything they could ,nothing worked.
any idea what is the problem?