Once you download the WhatsApp 2.12.15 version you will see a revamped user interface with three tabs for calls, contacts and chats unlike the old version which has only two tabs for contacts and chats.
Sadly the version of WhatsApp on Google Play varies from device to device so you will have to check up your version number by going to Help > About and continuously upgrading it to the latest version. You can also download the APK file from from WhatsApp’s website and sideload it onto your Android smartphone. Do remember to enable the Allow Installation from Unknown Sources option in Settings > Security if you want to install the APK directly. The version on the site reportedly brings voice calling too.
To place a call, tap the Calls tab and then the new call button at the top of your screen. Then, select a contact to call your near and dear ones over WhatsApp. Do remember to tell them to download the latest version from Google Play. As we reported two days back, iPhone and Windows Phone users will also be getting WhatsApp calling feature in about two weeks time.