The leaked icons come from a dutch android website. They sport a flat look and seem to be a part of the dialer, while showing some similarities with the stock Android dialer app’s call log. As for the leaked screenshot, it shows an incoming call, but still appears to be an early unfinished version of the app.
Leaked app icons
Voice calling is indeed the only feature WhatsApp needs right now, that will make it bigger than the current competitors out there . Viber and Skype offer voice calling along with messaging features while WhatsApp only deals with messaging.
Incoming call screen
Whatever it is, Jan Koum promised that the functionality will arrive before February next year. Lets just hope that the app gets a revamp as well as it is getting a bit too old, going purely by the looks.