WhatsApp Calling lets you call your friends and family using WhatsApp for free, even if they’re in another country. Currently, WhatsApp Calling is available on Android, iPhone, Windows Phone and BlackBerry 10.
WhatsApp Calling uses your phone’s Internet connection rather than your cellular plan’s voice minutes. Data charges may apply.
Important: You cannot access 911 and other emergency service numbers through WhatsApp. You must make alternative communication arrangements to make emergency calls.
To make a WhatsApp call, simply open the chat with the person you wish to call and tap on the phone button on top.
When someone calls you, you will see an incoming WhatsApp call screen. You can tap Answer button to answer the call, or Decline button to decline the call.
Learn how to use WhatsApp Calling on: Android | iPhone | Windows Phone
Cheers,
WhatsApp Support Team