Whatsapp has always been the best messaging app for cross platform devices like ios, & android . We also have heard about the coming feature of WhatsApp that WhatsApp is going to launch its calling feature . And yes its out now.

But calling feature is not available in the apk at play store. But Still you can enjoy this feature by following step by step method.
Steps to activate calling feature in whatsapp : 

download the terminal app and install it  from Here .
Now open terminal and type su to grant root access.

Then type am start -n com.whatsapp/com.whatsapp.HomeActivity and press enter

VOILA..!! Voice call feature is activated.

Requirements :

Your device needs to be rooted if it not search on google that how to root "your device name".