Oh, and it’s owned by Facebook! 🙂
Now, I personally don’t use WhatsApp that much right now. The people who I want to message are primarily using iMessage, Facebook Messenger or Wire. (And every once in a great while I’ll fire up Skype on my iPhone.)
But obviously there are 800 million people who do use WhatsApp each month… and they now have free calling! (If they are on Android, iOS or BlackBerry 10… and subject to a staggered rollout, i.e. people will get the actual ability to call over the next while.) It will be fascinating to see how this plays out.
If you are interested in some technical details and in what has the WhatsApp in common with the WebRTC, you can find an interesting post on https://webrtchacks.com/whats-up-with-whatsapp-and-webrtc/