According to suggestions from various blogs, the users need to download the most recent version of WhatsApp or get version 2.11.528 from the Play Store from the WhatsApp site to activate the feature.
As per AndroidPolice, the voice-calling can be actuated by accepting a call from somebody whose voice-calling is as of now activated. After you get the call, you have to close and afterward reopen the application. After that, as instead of seeing the latest talks, you will get three tabs specifically Calls, Chats and Contacts. The call tab shows incoming, outgoing and missed calls at the exact times.