Molly Woods describes a number of smartphone apps that can help protect your privacy in this New York Times article. Here are two snippets from her comments:
Android currently has the best options available for secure messaging. My favorite is the free TextSecure from WhisperSystems. It encrypts text messages between users, as long as you both have the app installed and you use it for texting instead of your regular app. The texts are encrypted as they’re sent back and forth and stay encrypted when they are stored on your phone.
If you want encrypted messaging across iOS and Android, try ChatSecure, created by the Guardian Project, a collection of developers, activists and hackers who create tools for more secure communications. This free app doesn’t replace texting; instead, it lets you send encrypted messages over a number of existing chat services like Facebook Chat, Google Talk, Google Hangouts, Jabber and some others.
You must have an account with one of those, and your recipient must also install ChatSecure. But since the app is free and available on virtually any device, it’s a good way to encrypt messaging across some common chat services. ChatSecure is also open source.
Read the full article on NYT.