Because I Am Bored

The Free 900 Number
Theory

Use a calling card to call up a 900 number or any number that bills you. Since you are calling a switching network which charges you already in the form of minutes on a pre-paid calling card, if you call a 900 number or any number that bills you, you are connected for free! The reasoning is because numbers that bill you directly require a form of caller-ID in which, when calling directly, they use to bill you. They find your number in a computer database, find your address and phone service company, and then charge you via notifying your phone service. If you use a calling card, because you are calling from a switching network which has its own number, they will be unable to trace the call back to you and charge you.

Reality

Calling Card companies make it impossible to call 900 numbers via calling cards. They will simply play that little recording that says "This service is unavailable."