Voice calling is definitely, definitely coming to WhatsApp and what's more, it's round the corner. A reference to the feature was spotted in the latest iOS update to the app by NDTV Gadgets, an Indian news portal.
There's no mention of the feature in the app's release notes, presumably because it's not active yet, but if you haven't granted WhatsApp access to your microphone, you'll get a pop-up, which reads: WhatsApp requires microphone access to send Voice Messages, record Videos with sound, make and receive Voice Calls.
According to NDTV Gadgets:
This pop-up will appear only if users have not allowed WhatsApp access to the microphone. To see this, go to Settings > Privacy > Microphone > WhatsApp > flip the slider to Off. Now open WhatsApp to find mention of the voice calling feature.
WhatsApp is the messaging app of choice for more than 600 million people around the world. It has single-handedly destroyed the SMS market in many countries, so having voice calling in its arsenal could be a game-changer. [NDTV Gadgets]
Top image: NDTV Gadgets