iPhone 5 "No Service" problem? Disable LTE.
If you have noticed your iPhone 5 goes into "No Service" and cannot connect to network, you might want to try to disable LTE.
Go to Settings -> General -> Cellular -> Enable LTE -> Off.
It happened to my wife's iPhone, and I almost wanted to bring the phone to service centre, but after searching online, I tried this method and ever since then, the connection has been fine.