Scenario: Your calling card balance is depleted, or worse, your auto-recharging calling card has been over-used, leaving you with a huge phone bill.
Scam: No one from your family or company recognizes the numbers or recalls making those calls.

    The only information that a fraudster needs  to make long-distance, domestic or international calls at your expense, is your PIN and calling card number.  - Phonecarddepot.com Fraud Team

Be careful around  airports, hotel lobbies, and other places where pay phones are located and people frequently use calling cards. Theives might look over your shoulder as you dial, or use binoculars or camera zoom lenses to observe you.

Protect your PIN:  When you use your calling card at a pay phone, shield the key pad with your body to prevent others from watching you dial. If you are verbally providing your number to an operator, speak softly so no one can overhear you.

Guard your calling card carefully:  If you order your calling card online from Phonecarddepot.com and print out or write down the PIN number to take with you.  Think about mixing up PIN digits to intentionally mislead anyone who may steal or find your card lost.  Be sure not to leave your card out in plain sight and make sure no one has access to it who isn't authorized to use it.

Buy many small value cards (non-rechargeable cards):  Instead of rechargeable or large dollar value calling cards, buy one time use cards below $30.  This mitigates your risk of loss due to theft or loss.

If you notice suspicious charges:  If there are any suspicious charges, call the calling card provider.  They can look up the numbers that have been dialed from your card and catch the culprit.

Unless you know who stole your calling card number, law enforcement authorities probably can't help you. But if you suspect that the crime occurred in a specific airport, hotel or other facility, notify the management.