Viber is totally free to download and has no hidden costs, in-app purchases or in-app ads. It's fully compatible with iOS 3.X and 4.X on the iPhone – partially supported by the iPad and iPod Touch – and is coming soon to Android, Blackberry and Symbian operating systems.
Unlike other popular VoIP apps, Viber isn't a battery hog; you can leave the app running all day without it draining your battery or heating up your iPhone. It also offers Bluetooth support so you can switch in and out of Bluetooth at any time with your headset. Check out the Viber's promo video below.