Viber is a voip app for Android and iOS devices (BlackBerry app is rumoured to be coming soon). Unlike other voip apps such as Skype, viber requires no registration. Following install you sign up via a text message and that’s it, you’re set to go.
The device can search your contacts and tell you who has Viber installed with a little icon beside the name (see picture). Unlike Skype you can only call/text other Viber users. All calls and texts are free to these users but remember the app uses data so if you’ve only a small amount of data on your monthly plan you could use it up very quickly.
As a replacement for Skype, Viber is excellent as you’re up and running so quickly.
Get it here: Viber