The process isn't as simple as updating WhatsApp to start using the voice calling features. It involves a couple more steps that you need to follow. We've described these below, so take a look to enable voice calling on WhatsApp for Android.
Download the latest version of WhatsApp for Android from here. The latest version on WhatsApp's website is 2.12.7, but if you're downloading from Google Play, ensure that your device has version 2.11.561. Older versions don't support this feature for all users.
Once you have the latest version of WhatsApp installed on your Android phone, ask someone who has WhatsApp calling enabled to make a WhatsApp call to your number.
Multiple users have reported that giving a missed call doesn't work. You'll have to receive the call and wait for a few seconds before disconnecting to activate WhatsApp voice calling.
When the feature is enabled on your smartphone, you'll see a new three-tab layout on WhatsApp, one each for Calls, Chats and Contacts.