[iMore Question]

I have it in a mophie charging case. The phone is almost 3 yrs old and has been working fine up to now. I powered it down for a flight tonight and when powered up (at my home location where it has been working great ) it never got out of "searching" mode, looking for cellular coverage. I have received texts, but could not send.

[Ledsteplin]

Welcome to iMore! It may be a weak signal. As to why, I have no idea. Could be your provider or an issue with the device. Check with your cellular provider and see if they have issues. Try a hard reset.
Hold the top or side power/sleep button and the home button at the same time until the Apple logo appears, then release.

[comiken205]

Cellphone service could be down? Do what ledsteplin said or put it into airplane mode wait 10 seconds and then take it off airplane mode. That has happened to me a few times and the airplane mode reset it.