Whatsapp was already popular with texting and it has now released its voice calling to extend to new areas. But there is a catch for now that it needs version 2.12.19. You can download the apk for that version online or just go to the Whatsapp site for it.
Once you download the apk file and just install it. You will notice the change in the UI and the addition Calls functionality enabled there. Whatsapp did give the update out some time back but it was not available to everyone. And the only way to try the feature was for one users having the feature to call another. But this update puts a end to all that and everyone who uses this version of Whatsapp can now try the feature. If you are interested you can download the apk for the link below or you can also wait for it to come on Play Store from where you can easily update and use the new feature.