With WhatsApp Calling, you can place a call to your friends 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.
Learn more about WhatsApp Calling on : Android | iPhone | Windows Phone | BlackBerry 10
Important: you cannot access 911 and other emergency service numbers through WhatsApp. You must make alternative communication arrangements to make emergency calls.
Cheers,
WhatsApp Support Team