The feature is automatically enabled to all users updating to version 2.12.5 of WhatsApp via the Play Store, which brings a revamped user interface sporting three tabs: Calls, Chats and Contacts.

All you have to do is tap the dialler icon that is available in-chat, or heading to the Calls tab and selecting a contact you wish to call. Both parties need to be on the latest version of the app for the voice calling feature to work.

The call function turns WhatsApp into a Skype without pictures, although it still cannot call landlines yet and you have to pay for it. Or at least I am supposed to but haven't yet.