Just to muddy the water - there are forms of text that use the internet used by hams but as others have said there is radio solutions that do not use the net. The simplest form is a coded voice transmission, the method I prefer is to use a common phrase that is code for something. “Aunt Sadie went to the Doctor”, actually means something else. Uses a one time cipher key. That requires planning and prepositioning.
I’ve worked out dynamic code systems independently. They don’t conform to standard codes. If we do codify a survival plan then various key words could shift dynamically. It would be like ‘one time’ ciphers but better.
It would be incredibly helpful to rapidly relay text, especially if transmissions are brief.
Thank you again for the info!