Answer for: After updating iPhone 6 to iOS 9.2, it lost signal; it only shows the company name but no signal.

 I had this problem on an iOS 5S device from a different carrier, I changed the SIM card, adjusted the network settings, and even did a factory reset, but the problem persists.
I manage to fix it every now and then by putting it in airplane mode, then turning it off, and it rescans the signal and works normally. But then the same problem reappears...