I believe, finally things started to change and 'apps' from mobile world started to enter 'desktop'.
I always believe, there is a limit to mobile/tablets and replacing laptop/desktop would not be possible in the near future. It may happen in one day in the future but not so soon. Tab/Mobile are good to 'read' but to act, we still rely on notebooks/desktops.
So when I saw the announcement, it's kind of wow to me. Mainly we've been used to an application on Desktop, then eventually see it on Mobile. But this is kind of odd
I've taken couple of screen shots of the interface and looks pretty simple, and straight forward. No bells, whistles, and no "call out" or "skype out" functionality like where you can call landlines/regular mobiles.
So it's still closed to Viber alone. I guess, we can see an option to 'pay' to make outgoing calls to regular PSTN or Mobile phones soon. Basically, this is where they can make some money from VoIP users. Like Skypeout or Fringout or even Google Voice ;)