Onionphone is a native Android application for anonymous, end-to-end encrypted push-to-talk voice and text communication over the Tor network. No servers, no accounts, no phone numbers — your .onion address is your identity.
Cross-platform compatible with Terminalphone — call between Android and Linux/Termux using the same protocol.
Optionally use your connection as a relay for ephermeral group channels.
Find the release page for version 1.0.2 which supports custom bridges for accessing censored networks.
Plain speech can be compressed pretty well. I'm not an expert by any means, but I suspect latency would be the bigger issue.
Latency is a huge issue, but it goes away with the PTT model. I tried full duplex on initial prototyping but it was trash.
PTT solves this by simply forcing the listen, digest, then respond. You can expect about 2-3 seconds of delay from when you release the ptt, to when the other side hears it.