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If you see a missed cell phone call from an unknown number and call them back, hold on to your wallet before you get taken by yet another scam.

Cell phone users can quickly lose $20 or more if they are hit up by scammers who are playing one-ring games with our cell phones.

The fraudsters get computers to send thousands of calls to random cell phone numbers, ring once and disconnect.

If you're curious about the missed call, you might return the call right away. But then, you're going to be charged $19.95 for an international call, according to the Better Business Bureau Serving Eastern Michigan.

After that, there's a $9-per-minute charge. Music plays to make it appear you're on hold and drag out that call.

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Origins: The "one ring" telephone scam is similar in form to the venerable 809 area code scam in that both involve trying to dupe unwary phone customers into calling a foreign phone number in order to stick them with hefty charges. While the 809 scam involves sending pages, faxes, voicemails, or e-mail messages that supposedly relay important information (e.g., news about a distressed family member or a notification of prize winnings) in order to lure the recipient into calling a provided phone number, the "one ring" scam employs a simpler technique: the scammers place calls to blocks of phone numbers (sometimes with the use of robo-call devices), disconnect each call after a single ring, and hope that the owners of some of those numbers will be curious enough to call back:
Dubbed "one-ring hang-ups," the scheme targets millions of mobile-phone lovers. Unscrupulous operators make thousands of random calls from normal phone lines, letting the phones ring once before hanging up. They count on inquisitive folk, or those anxious not to miss a single call, ringing back the number shown on their screens.

It's certainly not true, as stated in the example cited above, that the mere act of calling a particular number would allow a phone user's contacts and banking information to be stolen by someone else. That sort of information would be compromised only if another party somehow hacked into the user's phone (via a malicious app or other code) and/or the user actively did something to enable access to it. (In either case, there's no obvious reason why such a scheme would require the victim to place a call to the information-stealer rather than the other way around.)

Some versions of this warning maintain that "You may also be charged a monthly fee for joining some club you know nothing about. By calling the number, you 'authorize' them to place a fee on your cellphone bill." However, it seems to be more the case that victims aren't subscribed to services simply through the act of calling a phone number, but rather that the scammers use social engineering techniques (including harassment) to persuade them to subscribe to pay services or give out their credit card information:

Those who do [call back] find themselves listening to advertisements for all sorts of dodgy services. Some firms try to hook callers into subscribing, say, to high-priced chat-lines or Internet services. Others dupe callers into providing credit-card numbers. Using caller-identification in reverse helps to harass more users. Some victims decide it is easier to pay than face fresh hassles. Even if only a small fraction are snared, it is still a lucrative ploy: their own charges are small since they never give their quarry a chance to answer.