The feature was first tested for selective users and then launched. However, one needs to get an invitation from WhatsApp to add on the feature in his or her mobile messaging application.
Earlier, users whose voice-calling feature was activated had the advantage of passing the invitation to their friends by making a call through WhatsApp, but the invite feature was later on removed.
Android WhatsApp users with version 2.11.528 from Play Store or 2.11.531 from website, who are able to see caller icon on the app, can easily make a voice call to their friends.
The WhatsApp website, however, claims that the users can also pass on the invitation to others.
Other messenger apps which provides voice-calling facility are Hike, Viber, Line, Nanu, among others. But, WhatsApp that reportedly is the much famous messaging app than others, attracting around 70 million active monthly users, can add another edge to its user base in India with this add-on feature.