Good luck, dumb phone means no encryption, SMS and MMS are stored plaintext and freely shared with US three letters and phone convos have been spied on en masse since the 80s.

That wouldn't be an issue, if say, the dumb phone existed for emergencies only.

you'd have to give up phones

I did mention that as a possibility

Realistically you'd need to fall back on the postal service, but people can steam open letters

Well there's always carrier pigeons and jungle drums.