Signal Encrypted Text App. You already know it’s an end to end encrypted app. The signal private messenger was the first app for ios that allowed users to make easy, strongly encrypted voice calls for free.
Unlike other text messaging products, signal’s code is open source, meaning it can be inspected by experts, and the app also supports forward secrecy, so if an attacker steals your encryption. This can be a huge advantage for those of us who don’t want to pay for sms text messages and phone calls, or who want to make free international calls. You already know it’s an end to end encrypted app.
It does this by using push notifications to start the call and then using the zrtp protocol to encrypt it.
In addition to direct messaging, the app supports groups of up to 500 individuals, and optional encrypted messaging using the signal protocol. The app is free, but a premium subscription unlocks. Signal app doesn't require a login, usernames or pins. It’s only you and your correspondents who can see the respective messages.