They say talk is cheap. Google thinks it should be free. Google Talk enables you to call or send instant messages to your friends for free-anytime, anywhere in the world. Google Talk offers you:

Choice: Get in touch over email, IM or a call
Quality: Talk through your computer but hear your friends as if they were in the same room
Convenience: Your Gmail contacts are pre-loaded into Google Talk so inviting or talking to your friends is just a click away.

Download: Google Talk v1.0.0.104 (Freeware)
View: Google Talk Homepage
Source: MSFN