Works on phones as well, I'm told. To be frank, I've never been too impressed with Skype's image quality or sound - although I didn't use it often anyway. As with all such apps, it has to be installed on both the sending and receiving device in order to work. But hey, it's free, and works on even WiFi, 2G and 3G networks. Reviews seem to be good, although some still swear by Skype or other apps. But if you do this sort of thing, you might want to consider it as a backup when Skype support is discontinued.
It's VOIP, as are the others. Android users seem to like it, for what that's worth.
