How can I make unlimited US and Canada calls through my PC. Is there any special offer calling cards?

Calling Cards
email_01234 asked:

I am Residing at India and I need to make US and Canada Calls. The PC to phone calling cards are too expensive. Is any company offer unlimited PC to phone calls with a low monthly fee or FREE. How can I reduce the Charges. Or anybody guide me, How can I make US and Canada Calls at low rates.

Thank You