RedPhone For Android
If you want to be sure that no one's listening in or intercepting your messages, it's time to pick up the red phone. RedPhone for Android uses the phone's normal dialer and contacts to place calls as usual. If the person on the other end also has RedPhone, the app offers the caller an option to switch to a "secure line" and then jumps to Wi-Fi or the carrier's data plan. RedPhone is free, open source and available for Android only; an iOS version is in the works.