WhatsApp users are making more than 100 million calls a day using VoIP
Two of the app's largest markets are India and Brazil, where the ability to make these VoIP calls are a big draw. In India, 95% of smartphone users are employing WhatsApp, and in Brazil that figure is 94%. Those worried about running through their data can use a setting in the app that lowers the quality of the call by reducing bandwidth consumption. The calling feature does work on 4G LTE, 3G and 2G pipelines.
WhatsApp has over 1 billion users globally. Facebook closed on its purchase of the messaging app in October, 2014. By the time the deal was finalized, the value of the transaction exceeded $21 billion.