Earlier, when you wanted to call Europe from the US, needed dedicated trans-oceanic pairs of wires to be laid per individual callers. Thousand pairs of such wires would cost a real lot. And the lines would always be busy. Therefore calls were expensive then.
Now with the introduction of satellites n stuff, the costs have come down, but still phone companies charge you more for international calls.
With the Internet, and with sufficient bandwidth, you can modulate your voice over IP, and there are several calling cards that are available for making international calls. What you do is, you just call the local number, or possibly a toll free number connected to your local exchange, and then dial your international number. The calling card provider then transfers your call to the international destination thru VOIP.
Calling cards offer better audio quality, and reduces the delay between conversations.
You have a wide choice of International calling cards. How do you choose which is the best? You should look for a portal such as http://www.getmecallingcards.com/ which offers a huge choice of international calling cards at great rates.