Before you start to think Facebook will take over the world, look again at new competitors emerging in Asia, including this one originally from Japan and now boasting more than 100 million users.
LINE has everything you'd want in a mobile app: free text and voice (and probably soon, video), cross-platform versions (iPhone/Android/WinPhone, Mac/PC), and plenty of cool features like a way to sign in to your desktop using your phone (perfect for situations, like at an internet cafe, where you don't want to risk typing your password into a key logger).
Think of it like a cross-platform version of iMessage, or Path, or even Skype. There are numerous in-app purchases, including "stickers" that are apparently must-have for serious users.
The competition, internationally, for mobile and social apps is just unbelievable, and don't expect it to lighten up any time soon.
Feel free to add my to your contacts: my username is 'sprague'.