WhatsApp appears to have opened its voice calling feature to all Android users, with the invite window now open for several hours. The world’s most popular messaging app has been gradually rolling out this feature by opening the invite window only for a few hours at a time. This time however, WhatsApp may have opened the floodgates, reports Android Police.

The report says that many people have been receiving the WhatsApp calling feature on their Android smartphones. 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. After you get the call, you will see WhatsApp’s interface switch from just showing recent chats to three tabs – calls, chats and contacts.

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. These numbers of course don’t reveal the actual number of WhatsApp users because anyone who installed the app once is counted in this number. The number isn’t reduced if the person proceeds to delete the app. Even then, the number shows just how popular the messaging app is.

Earlier, the voice calling feature was rolled out to some users, but the invite window was closed before most people could get the feature. 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.

Having established itself as the world’s most popular messaging app with over 700 million monthly active users, WhatsApp seems to be augmenting its offering by adding features available in competing messaging apps. 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.