For some reason this morning I noticed my phone did not have a signal in my office, where it normally does. I went to settings, about phone and status and saw it had signal strength but was not connected. I then noticed that it said the network was T mobile. A simple power on/off got the phone back to At&t and working again, but I am wondering why it was on the T mobile network. Is there something I could have accidentally done to switch the networks. Anyone else have this happen?