BEST SERVICE FOR PRIVATE TEXT AND VOICE CHAT
Signal, which was created by unifying the apps RedPhone and TextSecure, is often credited as the app that got this whole end-to-end encryption thing rolling, and the one most often recommended for private chat since it is open source and free. Many of its competitive apps use what has become known as “the Signal protocol” for private messaging.
Unlike a lot of open source projects, it’s also extremely user friendly, with an interface every bit as accessible as something like WhatsApp. It uses your existing contacts list, and will automatically make encrypted connections if it detects the person on the other end has Signal.
Recommended alternative: Threema ( threema.ch) has a similar level of security and ups the ante with completely anonymous user accounts.