[rg3]

If you already have an Android phone, I guess the RedPhone app is the most convenient and cheap way to make encrypted voice calls.

https://play.google.com/store/apps/details?id=org.thoughtcri...

[jeffrey8chang]

The other party you called must use Android phone + RedPhone app as well.

[13throwaway]

Redphone can talk to iPhone users with the signal app.