Skype is the best-known VoIP but Gizmo Project is equally (if not better) than Skype. I use both services and each has it’s strengths and weaknesses. I prefer Gizmo because it’s more fun (build in sound effects) less expensive than Skype. But, Skype seems to have a better connection and less dropped calls than Gizmo.
Gizmo Project 3.0, located at http://gizmoproject.com. Gizmo Project 3.0 introduces meta-voice capabilities, which enable free calling to Yahoo Messenger and Windows Live users. Gizmo Project 3.0 is the first VoIP software to link together multiple popular VoIP networks.
Built by the inventors of Kazaa, Skype lets you make free VoIP calls via your broadband connection. The service uses a peer-to-peer networking scheme, but rather than sharing files, connected PCs help route one another’s calls. Skype also uses that routing technology to get around the need for (and cost of) central servers and directories, so call delivery can be free.
Popularity: 12% [?]