Along with all the other stuff you can do in the World According to Google, you can now make phone calls. While you may be used to searching the web, viewing breaking news, using Google Docs productivity tools, and of course taking advantage of the the omnipresent Gmail service, you can now make free phone calls.
To take advantage of this service, simply log into your Gmail account, open the Chat menu, and click on "Call phone". This service takes advantage of the Google Voice infrastructure to let you complete calls–free to US and Canadian numbers–right inside of Gmail. You do need to install the voice and video chat plugin for your browser, which is compatible with systems running Linux, Windows XP and later, and Mac OS X (Intel only, not PowerPC). Once you've done that, you can start making your free VoIP calls.
Google anticipates that this service will remain available (and free) through at least the end of 2011.