Make free phone / video calls within Canada and the United States using your GMail account and Google Voice.
See this blog for more details:
http://googlevoiceblog.blogspot.com/
To make a call, just click the Call phone link in Gmail and enter any number.
You need to have working speakers and a microphone. Optionally you would need a video camera for the Video Calling portion.
As of August 28th, this is not available for Google Apps, but its only a matter of time before it is available.