A Calling Card is very different from your Long Distance Services. A Calling Card is what you use when you are away from home. Sometimes this is a physical card, and other times this is an access number you use in order to make your calls from a pay phone or another telephone other than your own. The biggest difference is the rates. This is an especially good opportunity for students, sales representatives, travlers, etc.
Cards are also available to other countries outside the USA, rate information is provided.
Just enjoy the savings. But as always, you may also become a representative for this service and earn some spare money for the effort.