Calling from Gmail now in 38 languages, with lower rates to over 150 destinations – Official Gmail Blog
August 2, 2011 May 25, 2015
I suppose it’s a bit like Skype, difference is that there is no connection charge!
Check out the rates here : https://www.google.com/voice/b/0/rates
You’ll need to install the voice and Video plug in : http://www.google.com/chat/voice/