The WhatsApp iOS app update (version 2.12.1) also brings new features such as sharing extension, quick camera button in chats and other additions apart from the VoIP-based voice calling feature.
The App Store listing notes that WhatsApp Calling will roll out to all users slowly over the next several weeks.
Another major highlight of the v2.12.1 update is the addition of iOS 8's sharing extension that enables a user to share images, videos, and links to WhatsApp contacts from any other app. The update also adds the quick camera button in chats that allows users to launch the camera button right from the chat screen to share with contacts.
Other additions include the ability to edit contacts from the WhatsApp app, send multiple videos at once, and options to crop and rotate videos before sharing them.
Recently, WhatsApp's CEO and co-founder Jan Koum claimed that the app crossed 800 million monthly active users. The company had crossed 700 million active users in January and thus adding 100 million users in four months.
While the feature is now available to Android and iOS users now, those on Windows Phone platform continue to wait. Earlier this month, the WhatsApp voice calling feature was said to be in development for the Windows Phone platform.