here are some...
*voipstunt.com
*voipbuster.com
*skype.com
*www.gizmoproject.com/
*phonehog.com
now here is a neat trick...
although VoIPstunt provides free calls to these countreis...
Australia
Austria
Belgium
Canada
Chile
China
Croatia
Cyprus
Denmark
Finland
France
Germany
Gibraltar
Hong Kong
Hungary
Iceland
Ireland
Israel
Italy
Japan
Liechtenstein
Lithuania
Luxembourg
Malaysia
Monaco
Netherlands
New Zealand
Norway
Poland
Portugal
Singapore
Slovak Republic
South Korea
Spain
Sweden
Switzerland
Taiwan
United Kingdom
United States
u can also use phonehog with it which cud not be used through Skype!