WhatsApp has released its new feature of VOIP voice calling to all Android users, with the invite window now open for several hours. This move appears to have come on the back of another milestone for WhatsApp - over 1 billion installs via Google Play. The app's Google Play page now shows that it has between 1 billion and 5 billion installs. To activate the feature, all you need is the latest version (v2.11.561) of WhatsApp (via APKMirror) and a WhatsApp call from someone who already has the feature (we are giving away free invites). After you get the call, you will see WhatsApp's interface switch from just showing recent chats to three tabs - calls, chats and contacts. Although WhatsApp still has not announced the voice calling feature officially on its website or the release notes on Google Play. WhatsApp for iPhone still doesn't have this feature even though a voice calling button appeared in the app some time ago. (read our guide for iOS users) The report says that many people have been receiving the WhatsApp calling feature on their Android smartphones. WhatsApp for Android users also recently got a Web version that works well. Both these features have been available for some time with competing messaging apps such as iMessage (calling via FaceTime), Line, Viber, among others. Need an invite? Drop a comment below!