WhatsApp is the closest thing we have to a universal chat client. All you need is someone’s phone number to start gabbing away, just as easily as you can with traditional SMS messages.
This has helped WhatsApp become the dominant messaging app on the planet, with more than one billion users. As popular as it is here, you’ll see the phenomenon is far more pronounced when you travel outside the United States. In many other countries texting plans aren’t free, so smartphone users have bolted to the WhatsApp cloud for simple and universal messaging, since it’s also available on iOS.