I don't think you can have security on a device you don't have root access. And since most of the phones are locked and untrusted does it matter how much exactly?

And almost all really nasty regimes have already somewhat liberal view of using thermorectal cryptoanalysis anyway. Tor style obfuscation and retransmission with very low SNR masked as a torrent client could be a better way to go. If your government know that you said something to someone they can just "ask" you to find exactly what. The trick is not to be found.