You can make international calls for free. Actually you will not be able to make calls but you can receive calls for free, which will cost others their local call charge. I just tried with US and and it worked fine.

Here is the list of countries supported. Add phonenumber@talkster.gtalk2voip.com where phone number will be including country code, example for USA , use 12125551212@talkster.gtalk2voip.com, a window will come with details. You can see step by step here