I saw an item earlier this week on the France 2 news that I found interesting. A group of telephone scammers were found and arrested, stopping a huge — but not surprising, and not unique — callback scam.
Here's how it works:
The scammers set themselves up with pay-to-call telephone numbers. They use computers to automate the process, and they call people's mobile phones. But they don't let the calls complete: they ring the phone just long enough for the caller's number to show up on the telephone, but they disconnect before the victim could possibly answer. The victim, curious about who called, calls back and gets a recording of music. What the victim doesn't know is that he's just paid a little less than a euro for that call, about half of which goes to the telephone company and half to the scammers.
They made many millions of calls, got about a 33% callback rate (yow!), and earned a little less than 50 cents per callback. All told, they snagged about EUR 600,000! [So, doing the math, that means they made around 36 million calls and got some 12 million callbacks.]
This made big news in France because they were caught and stopped, and because of the scope. But this is certainly not the first time this sort of things has been done. There are lots of stories about people leaving messages to call back pay-to-call numbers, and caller-ID features just make this easier: the scammers avoid the need to leave a message (which takes time and requires that the user not be there to answer), allowing them to achieve a far higher call rate; in exchange, they accept a lower callback rate (people are more likely to call back in response to an actual message), though 33% is certainly quite amazing (and lucratively high).
Now, the defense against this sort of thing is obvious, and I'd not have a problem with this myself: just don't call back. I haven't the time nor inclination to call back an unknown number whose caller didn't leave a message. (In fact, I don't even call back on actual messages unless there's a compelling reason for me to.) Clearly, though, I'm just one of the 2/3, and the 1/3 whose curiosity is piqued easily gives a great return for the scammers.
On top of that, the cost to each curious user is small, so they probably don't mind terribly — it's not so bad to pay 85 cents to satisfy one's curiosity. (On the other hand, they were caught because some victims did complain to the telephone company, and that triggered an investigation.)
So don't fall for it. If you see an unknown number on your phone, and they don't leave a message... just shrug and put the phone away.