Think twice before returning that missed call: it could end up costing you a lot of money.

A new phone scam calls users without giving them enough time to answer, then tricks them into dialing pricey foreign chat lines.

The Better Business Bureau has issued a warning about the scam, which appears to be targeting mobile-phone owners in the United States. The trick would also theoretically work in Canada, although a loophole in U.S. trade law makes American users more tempting targets.

The one-ring scam works as follows: A computer program originating outside the U.S. dials American customers and lets the phone ring exactly once before hanging up. This is enough time to register on a phone's missed-calls screen, but typically not enough time for a user to actually answer.

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These calls are often from Antigua and Barbuda, Grenada, the Dominican Republic and other countries in and around the Caribbean. As with the U.S. and Canada, the country code for these countries begins with "1," which is often enough to fool unsuspecting Americans into thinking they're receiving domestic calls.

Calling back is generally not the best idea, as the lines connect to premium chat lines — usually involving phone sex. In addition to charging a $20 international calling fee, these lines also charge users for each minute spent connected.

The practice of adding unauthorized charges to a phone conversation is known as "cramming," and is illegal in the U.S. However, while the Federal Trade Commission (FTC) can crack down on this practice domestically, it cannot enforce U.S. law overseas.

If you find yourself with a trumped-up international calling charge, your only recourse may be to take it up with your carrier and hope that your representative is in a forgiving mood.

Simply receiving the missed call is harmless, so your best bet is to ignore any missed calls from unknown numbers, unless they're accompanied by a voicemail from a real person. As J.R.R. Tolkien pointed out half a century ago, investing your resources in One Ring can lead to ruin.

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