Software Update, or by connecting i Phone to i Tunes on computer and checking for updates there.Note that for some users the below tricks may resolve the “No Service” and “Cellular Update Failed” problem on their i Phone, but for other users it does not.
For some users this may be unacceptable as a permanent solution, but again this is a workaround, so you can decide whether or not the trade-offs of temporary disabling wi-fi calling and LTE voice are worth having a cellular data connection at all.
For many i Phone users, their cellular service will restore and start working again, though this comes at the expense of temporarily losing wi-fi calling and voice LTE.
If a new software update does resolve known cellular data problems with i Phone, then you’ll almost certainly want to change the LTE data setting back to Voice & Data, and enable wi-f calling on the i Phone again so that you can use those great features as usual.
Did the above tricks work to get your cellular data and cellular connectivity functioning again on i Phone?
Can I restore my i Phone 6s without updating to i OS 11?