Gizmo for Mac is a Free Phone for Your Macintosh – Gizmo makes calling as easy as instant messaging!
The Gizmo Project uses your internet connection (broadband or dial-up) to make calls to other computers. With the click of a mouse, you’re connected to friends, family, and colleagues anywhere on earth. It’s just that simple. You talk clearly. For as long as you want. Gizmo to Gizmo calls are free. You can also call any traditional phone using Call Out (Call Out calls aren’t free). Gizmo can also be used to IM with your contacts.
Gizmo for Mac requires Mac OS X 10.3.9 +, Microphone and Dialup or Broadband Connection