Morse code and some crypto material. Or develope your own language or fon-speak.
Or, only use key words or phrases guaranteed to perk the “ears” of computer aided SIGINT, inundate communications circuits with this SIGINT making it moot over the short term.
Use clandestine drops...
But a secure telephone? Smoke signals maybe...
The “wickr me” app is free and does phone calls as far as I know. I’ve only had it a few weeks and haven’t really used it except to text.
Thank you all!