In addition to its standard messaging features, WhatsApp allows you to make phone calls using WiFi or mobile broadband (data charges may apply). In order to use this feature, make sure that you have the latest version of the app installed on your device.
How To Make Calls on WhatsApp
Making phone calls with WhatsApp Messenger is easy and straightforward. In many cases, a WhatsApp call will be a cheaper alternative than a regular phone call, especially when both parties are connected to WiFi.
To make a call, simply go to Contacts. Select a contact and tap on the Phone icon to make a call: