Many iPhone users out there are already familiar with WhatsApp, a handy little app that allows you to send messages to other WhatsApp users for free. One of the benefits of the app is that it scans through your address book and automatically adds friends that are already using the service. Now Viber is doing something similar, only that it offers voice calls instead of text messaging. So, unlike Skype, you won’t need to create a user account and manually add your friends, since it’ll be able to do so automatically. You’ll be able to make calls over 3G and Wi-Fi, though you’ll need to make sure your data package offers you enough data or you’ll be facing a rather hefty phone bill. The app is currently compatible with iOS devices running iOS 3.0 or later and a BlackBerry and Android version is also on the way. Video after the jump.