Need something achievable for an extremely tech illiterate person on iOS. I got told about this after they are already gone and have no access to the device, but am asked to solve the problem.
EDIT: (SOLVED) Signal was super easy, works awesome, and was easy even for my mom to figure out on her own. Thanks
As others have pointed out here, Signal is a very good choice.
If they do not have cell service, they won’t be able to set up Signal, or any other service that requires a phone number (they won’t be able to receive the text message that verifies they own the number).