If you're in the US or Canada and calling any other country, OR if you're in any other country and calling landline or mobile numbers in the US or Canada, the standard SkypeOut rates apply.
So no, this does not give free calling to the US and Canada from overseas.
My guess is that Skype uses your IP address to validate that you are in the US and Canada, and their list of US/Canadian IP networks isn't quite accurate. It works for me.
They may be doing something silly like checking the country in your Skype profile, but I doubt that since it's easy for anyone to set that to whatever they want.
-- Mark --is two wolves and a sheep deciding what to eat for lunch. Liberty is a well-armed sheep contesting the vote.