[debt]

Sneakernet is the most future-proof solution. It's impossible to stop by design. It can be discouraged with arrest, but not stopped completely.

[jacobush]

Not completely non-workable either. A lot of store-and-forward text messages would fit on a 256GB USB.

[cbluth]

Something like an isolated wifi "dead drop", and a gossip protocol would be all you need, like ssb.