WhatsApp has officially enabled the Voice calls feature in their Instant Messaging app, for all Android devices.
You don’t even need to update the app to get this feature. It was added automatically, possibly using a server side switch.
You will notice a new tab named “Calls” to the left of “Chats” and “Contacts” tabs. This is where you can call your contacts from. However, you can also call your contact from the messaging, i.e when you have the conversation window open. Just tap on the Phone icon to call your contact.
Prior to this, tapping the phone icon used to prompt users to pick an app to make the call, but it no longer appears now. WhatsApp seems to have made their own dialer as the default dialer in the app.
If you do not find the calls tab, download the latest version of WhatsApp for Android, you can do so from the official website. The latest version is 2.12.19. You can install it using any file manager app of your choice.