cellular update failed And no service

We, of course, have absolutely no idea what “did all the steps” means.

If you see a Cellular Update Failed or Apple Pay Not Available alert after iOS update or restart - Apple Support

If you see No Service or Searching on your iPhone or iPad - Apple Support

I'm assuming you did the shut off and on, both hard and soft. I'm assuming you pulled the SIM card as well. I've experienced a similar problem with my iPhone 7, same model number. The issue is known to iPhone 7's.

This is my experience with it. I did all the steps and even went to my service provider, my provider was adamant that the only way to fix the issue was to upgrade, that wasn't an option. After some research online and through the apple support articles I have found that iPhone 7's with the model number A1660 may show a "no service" message. Apply says it is due to a failed component on the main logic board. The nice thing is apple provides a repair program for the issue but you'll have to go into an apple store or authorized apple repair business. iPhone 7 Repair Program for "No Service" Issues - Apple Support

At the time my phone had the "no service" issue there was the iOS 12 update. I could not update it myself at home for whatever reason, I tried doing it from the phone and the computer. I brought my phone to the store, they were able to update it and magically fix the problem.

However, just so you are aware, two weeks later I now have the message "cellular update failed." If you see a Cellular Update Failed or Apple Pay Not Available alert after iOS update or restart - Apple Support

iOS 12.1 is now available but I cannot download it due to network connectivity like "poor network connection." I have tried to update it from the computer as well as the phone.

TL;DR : Basically have to take your phone in for apple to repair and/or replace it.

baris291,

See this:

Update your carrier settings on your iPhone or iPad

If you can‘t make or receive calls on your iPhone

Good luck.