http://gmailblog.blogspot.com/2011/08/calling-from-gmail-now-in-38-languages.html?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+GoogleAppsBlog+%28The+Google+Apps+Blog%29
Gmail today announced on their blog that they have expanded Google Voice so that you can make calls via the internet. It works just like a PAYG/Skype, you buy credits, no connection charges and you just pay for the time you use.
Call prices (https://www.google.com/voice/b/0/rates)
You need to install the plugin, but it's a nice bit'o'kit and for someone like me who uses Gmail a lot it could be a very nice addition to the fold and save a chunk of dial time and possibly even save some money.