An update is required to use cellular data on this iPhone

Go to Settings/General/About and look at Modem Firmware. Is the entry blank? If it is you need to reinstall it by restoring the phone to factory settings, then restoring a backup. Back up the phone first, of course:

1. How to back up your iPhone, iPad, and iPod touch - Apple Support
2. Restore your iPhone, iPad, or iPod to factory settings - Apple Support - follow the instructions to restore using your computer, do not using Settings/General/Reset (which is not included in those instructions)
3. Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

If the modem firmware DOES have a value you may have a hardware problem. The first step is what I just posted, but after that you need to contact Apple support using the Get Support link at the top of this page.

Hi,

I did what you wrote there and it works great. /iPhone 13 iOS 17.4.1

BUT, after a few hours, the same thing happened. No Cellular but this time there are number 3.50.04 in the firmware. I restart the iPhone and the firmware disappears.

Is this something for the Support?

Thanks

I am facing the same issue with my iPhone 13. You found a fix??