WhatsApp has a commanding lead in volume of users over other messaging apps and services, but its competitors are nipping at its heels. There are at least 50 apps that offer free or nearly free text messaging. Line, WeChat and Viber, which was recently acquired by Japan's Rakuten for $900 million, are each hovering around 300 million users. Skype reported 299 million users last June, two years after it was acquired by Microsoft for $8.5 billion. Apple last reported it had 140 million users on its iMessage service. Kik Messenger and Tango each count about 100 million registered users while BlackBerry's BBM service, the pioneer in mobile messaging, is falling behind with 80 million users.
So what's so special about WhatsApp?