How to make a free call to any country in the world

How to make a free call to any country in the world ,recently I have found out this interesting website which is claim for making a free call to your friends in any countries .In my point of view I think this is not a bad Idea so,why dont take a chance if we dont have the choice .The step is so easy just follow the like below and do follow the easy 3 step below

http://www.rebtel.com/en/Learn/Make-Free-Calls/

Tell us where you’re calling from. Fill out the easy sign up form and tell us which phone you'll use to make your Rebtel calls.
1
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Tell us who you want to call. Enter your friend's name and international number and Rebtel gives you a unique local number for each friend. Create it once, save to your phone and keep forever.
2
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Ask them to call you back. Call your friend on the local number. When they pick up, ask them to hang up and call you back on the number displayed on their phone while you wait on the line. The call will be instantly connected and you can talk internationally for free. You only pay for the local part of the call to your regular carrier.