14 DAY TRIAL // Earlier this week, Apple released the third maintenance update for its iOS 12.1 mobile operating system for supported iPhone and iPad devices, versioned 12.1.3, which fixes a handful of annoyances, but also introduces a nasty issue.
We usually recommend our readers to update to the latest stable software version of their operating systems and apps as soon as possible, but if you haven't updated your iPhone to iOS 12.1.3, don't do it, because it may cause a "No Service" issue where you're left only with Wi-Fi and no mobile network/data.
It happened to me too, hours after updating to iOS 12.1.3, I was slapped with a "No Service" issue on my iPhone 7. After enabling AirPlane mode and then disabling it, the device wasn't able to find the mobile carrier, first displaying "Searching..." and a minute later showing "No Service" in the left side of the screen, next to the Wi-Fi icon. I thought it was just me, but it looks like more and more users are reporting this issue.
Here's how to temporarily fix the "No Service" issue on iOS 12.1.3
While Apple is yet to release a fix, I was able to resolve the "No Service" issue on my iPhone 7 with a little bit of patience. As expected, my first instinct was to turn on and off the AirPlane mode, but that didn't work. I also rebooted the phone, and that didn't work either, so I enabled AirPlane mode again (with Wi-Fi also disabled) and placed the device on its stand.
A few hours later, I turned off AirPlane mode and the "No Service" issue was still there, so I rebooted the phone again, and, finally, the problem was fixed. So, as you can see, there's no exact workaround for this unwanted problem Apple brought on us with the iOS 12.1.3 update, but you could also try resetting the Network Settings if rebooting/AirPlane mode combo doesn't work for you.
The "No Service" issue hasn't returned to this day, but I decided not to take any risks and upgraded my iPhone 7 to the first beta of iOS 12.2 until Apple decides to release another maintenance update for iOS 12.1 to fix the problem. I do not recommend you switch to the latest beta iOS update, as that may cause other issues as well, so all you can do is wait for a fix or try your hand at the workarounds mentioned above.