In 2011, when WhatsApp had "tens of millions" of users, the Financial Times said it had "done to SMS ... what Skype did to international calling." Now that the cross-platform messaging app has hit 250 million active users, that statement rings truer than ever.
WhatsApp is available for iPhone, BlackBerry, Windows Phone, Android and Nokia, so it's not limited to a platform like Apple's iMessage. The service lets you send messages to users on any of the supported platforms without paying anything except your standard mobile data fee (and, for some versions of the app, a one-time $1 fee). It has support for images, video messages, audio notes, group chat and more.
Even though it launched only four years ago, in 2009, WhatsApp's userbase is impressive in comparison to other communication platforms. Video-chat service Skype, which launched in 2003, had 280 million active users as of October 2012. As it marked its seventh birthday in March, Twitter celebrated 200 million active users.
Much of WhatsApp's popularity can be credited to international users, who face high SMS costs while texting across borders. As you can imagine, that kind of workaround to traditional carriers stirs controversy on a couple of levels. In addition to depriving carriers of "revenue from international calls and texts," a recent Reuters report said, communication on the app is hard for states to monitor. Because of this, Saudi Arabia plans to block WhatsApp "within weeks" if the firm doesn't "comply with requirements set by the kingdom's telecom regulator."
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