Your pager beeps, showing a strange phone number. Or, an "urgent" e-mail arrives asking you to call an person you don't know at an unfamiliar number. Should you call them back? Given a plausible explanation, many people will indeed pick up the phone and place the call, even to an unfamiliar phone number.

It could turn out to be an important call -- or, it could actually be an international calling scam. If you inadvertently call out of the country, you could find yourself facing a huge phone bill, even for a brief call. That's because each country sets its own telephone rates, and there's no maximum. Some scammers take advantage of this situation: by enticing you to call out of the country, they can charge you big bucks, and earn a cut of that profit.

When calling from the United States, it's usually easy to tell when you're dialing internationally: the phone number almost always starts with the digits 001. However, there are exceptions to the rule. Calls to Canada and parts of the Caribbean look like 1 + three digit area code + seven digit number, exactly like a call to anywhere the U.S. The Federal Communications Commission puts the problem succinctly: "While these telephone numbers may look like domestic long distance calls, international telephone rates apply."

You should be on guard when asked by a stranger to place any urgent call -- but be particularly skeptical if the phone number is in area code 664, 809, or 758. These are the area codes for Montserrat, St. Lucia, and the Dominican Republic, respectively: countries with international calling rates that may be excessive... even exorbitant.

The FCC also recommends that telephone customers be wary of advertisements for telephone entertainment services that claim "not a 900 number," "no premiums apply," or "LD rates apply." The service providers would like you believe that these numbers have no special charges -- but if they're in one of those area codes, they do.

Remember to check your long distance phone bill every month and report and unusual or unauthorized charges to your telephone company. Your phone company may provide a refund, although they are under no legal obligation to do so.