WhatsApp has been involved in A/B testing of Voice call feature for the Android platform for a couple of weeks. Meanwhile the same feature is being tested out for the iPhone too.
The Voice call feature on WhatsApp for iPhone is being tested on beta builds for the iOS platform. Minor user interface changes will take place to show the calling button right next to the contact’s name on the window.
When that button is hit, the voice call is initiated with a clear mention of the words – WhatsApp Call. Based on the beta testing, we can expect WhatsApp to make the calling feature available for the iPhone owners in the near future. Meanwhile, there is no sign of WhatsApp testing Voice Calls feature for Windows Phone platform