I have this old 5s and have moved to the iPhone 6. So when I retired the 5s it would cough up messages about no SIM or no Service.
YOU have to decide what you want to do about this. For me I follow the CNET Cheapakate and obtained a plan with Freedompop for zero dollars a month. This allowed me to activate and use my 5s as a backup phone with 100 minutes talk, 100 text messages and 100 megabytes a month which autostops when the data is depleted.
I did look through all the apps and set them to not use my cellular data which works for me on this phone.
I’m confused about when, if ever, I should be using celllular on my iPhone. I have a good wi-fi connection at home and a portable jetpak mini when i’m on the go. So I have not been enabling cellular in my settings but I get error messages telling me I don’t have it. Can you provide some guidance?