Earlier this month, we told you WhatsApp was testing voice calling feature for Windows Phone. At the time, it was only available privately on the WhatsApp beta testing program.
However, starting today, Windows Phone users can now use WhatsApp to make free VoIP calls to their Android and iOS counterparts. To get the new feature, you have to update WhatsApp for Windows Phone to the latest version.
The new version also lets you send audio files, as long as you're running Windows Phone 8.1 and above.