February 25, I wrote an article about an announced upcoming feature called Whatsapp voice. It will basically allow you to make a Voice Over IP (VoIP) call to any other Whatsapp subscriber. Sure VoIP is a crowded space but many of your friends are likely already on Whatsapp (with its 400M subscribers) which means this may get immediate traction.
iPhoneItalia (link) published the first leaked screenshots of this upcoming feature .
When starting the updated version, you will be prompted to permission to use your microphone. Like most calling apps, you have Mute, Message and Speaker buttons. I am guessing that bluetooth will also be supported but we'll have to wait and see.
Based on other leaks, we believe Voice calling will work on both WIFI and 3G.
Although the leaks only show an IOS 7 designed version, it is safe to assume Whatsapp will bring this to all of its other platforms (eventually).