WhatsApp Voice Calling lets you call your contacts using WhatsApp for free, even if they're in another country. WhatsApp Voice Calling is available on Windows Phone 8.1 and later, as well as on Android and iPhone.
WhatsApp Voice 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 Voice Call, simply open the chat with the person you want to call and tap on the phone icon on top right of the chat screen, then tap voice call.
When you receive a voice call, you will see an incoming WhatsApp voice call screen.
You can answer or ignore the voice call. Alternatively, when you are within WhatsApp you may reject the voice call by sending a WhatsApp message: tap reply with message and select a quick message.