The cards may be convenient, but the nation’s consumer protection agency, the Federal Trade Commission (FTC), warns that many prepaid calling cards have hidden fees and don’t deliver the promised minutes as advertised. Once you’ve paid, you may discover a problem that leaves you out of luck and out of cash.

The FTC has a few suggestions for avoiding difficulties:

* Look for information about maintenance fees, surcharges, fees for using the card at a pay phone, and extra charges for calls to a cell phone or toll-free number.

* Verify that you can follow the directions on the card.

* See when the card expires.

* Look at the package and in-store marketing for the card’s local and international fees. If you are unsure of the price, then think about buying another card.

* Verify that the card is contained in a sealed package or that the PIN cannot be seen. Otherwise any person can write down the PIN and use your phone time.

* Look at different rates. Extremely low rates, especially for international calling, may serve as a red flag that the card won’t actually deliver the promised number of minutes.

* Ask the retailer if it will back a card that fails to deliver the number of minutes promised.

* Locate a toll-free customer service phone number. If you can’t find the customer service number or if it isn’t a toll-free number, it may be difficult to get in touch with someone at the company who can assist you with problems.