If you haven't already heard of this (I had missed it somehow), check this interesting little thing out...

it must be the tiniest little communicator on the planet that allows you to text that doesn't require cell service.... (other than maybe Zoleo, which I have, which is useful on wilderness trips, but rather limited in functionality)

http://www.picoaprs.de/index_en.php

And it's actually being made and sold (see the list of websites where it is for sale shown in a top link at the site above).

YT coverage on this tiny thing https://www.youtube.com/watch?v=n4dKzOXvhGA

You will, it seems, need a ham radio license to use it meaningfully

Very interesting though.