Low speed, p2p, wireless as a secure alternative to SMS and Signal-like services.

[grarpamp]

> To be continued...

SDR approaches are quite strong there due to the natural lack
of centrally controlled physical constraints and spying upon the
physically fixed transmission medium (cables).

One can easily imagine a mobile messaging application
on a phone or laptop, jacked out via its USB port into an
inexpensive SDR dongle in a pocket / backpack / car,
tuneable for long distance (intercontinental) down to
short distance (neighborhood / city / region).

The SDR and gear can all be community specified,
wiki-howto'd, bulk crowdfund or off the shelf purchased, etc.

So long as you're not tacked up all the time broadcasting
pirate radio from a fixed location... extremely hard to find or shutdown.

Search things like SDR, gnuradio, ettus, pirate radio,
guerrilla radio, spread spectrum, encrypted spectrum, etc to get started.