The feature will be available to some select Apple devices. So, if you don’t see the feature on your WhatsApps yet, do not fret, the company says, it is rolling out the update slowly over the next several weeks.

WhatsApp has an active monthly userbase of 800 million, that’s an astonishing figure! Providing these users with free VoIP access means that a lot of global carriers would be decimated. The free WhatsApp messaging has already done enough damages, since most people no longer send SMS. In fact, it is worthy of note that the SMS revenues have plummeted over the last few years, since WhatsApp hit the mainstream.

Since Facebook acquired WhatsApp for a whooping $19 billion, they have tried to rebrand the service as not just a mere messaging app or SMS replacement service, but a more useful client that’s capable of solving some simple human problems.

VoIP is one of such cool features that eliminate a barrier. However, in developing nations, the service is far from best because of the mediocre network and slow data transmission in such nations. WhatsApp also launched the web client few months ago, that expanded the horizon of the service.
http://www.techrez.com/whatsapp-starts-pushing-out-its-voice-calling-feature-to-ios-users/