WhatsApp Calling lets you call your friends and family using WhatsApp for free, even if they’re in another country. WhatsApp Calling is available on Windows Phone 8 and 8.1, as well as on Android, iPhone and BlackBerry 10. Due to the limitations of the operating system we are unable to provide WhatsApp Calling for Windows Phone 7.
WhatsApp Calling uses your phone’s Internet connection rather than your cellular plan’s voice minutes. Data charges may apply.
Note: You can’t 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 want to call and tap on the phone icon on bottom of the chat screen.
When you receive a call, you will see an incoming WhatsApp call screen.
You can answer or ignore the call. Alternatively, when you are within WhatsApp you may reject the call by sending a WhatsApp message: tap reply with message and select a quick message.
Learn how to use WhatsApp Calling on: Android | iPhone | BlackBerry 10
Cheers,
WhatsApp Support Team