Using Google Voice, you will be able to dial to US/Canada for free. You can also add credits in multiples of $10 and then you can call to other part of world in nominal rates. I tried a US number and it was working :-). But why don't they offer similar free calls within India?
Though this service is not officially deployed by Google so sometimes this bot disappears sporadically and comes again (may be because of some kind of testing being done).
Overall it is a good news for many Indians whose friends and family are living in US. Enjoy!
Update: Since few days, I am unable to see the Google Voice bot in my contact list. Not sure what Google is doing with it.