Google just released a IM/VOIP client that allows you to send messages or voice call your friends.
It’s still in Beta, and you have to have a Gmail account to use it (though they’re working on allowing all email accounts access).
Looks like a good thing that I will be trying out. Send me a message or give me a call if you’d like to test it. My gmail account is in the profile.

Google Talk

Edit: I’ve tried this out, and the sound quality is amazingly good! Better quality than Skype or Gizmo Project, though it’s quite limiting in the need for a Gmail account, and the lack of support for conferences.
Soon though.