A company called Whisper Systems has made two Android apps to aid the paranoid: RedPhone and TextSecure. The apps allow you to encrypt calls and text messages, respectively, and are available through a public beta right now. [WhisperSys]
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The most overlooked feature of RedPhone is that it doesn't use any minutes to make a phone call. It's mobile VOIP and it's free (at least for now.)
That's enough to make me want to try it out.