You may also someday receive a call and hear a voice saying that your network operator's server has a malfunction, and that you are the only person who can fix that by entering a long USSD command. Don't even think about entering it. This command activates a special service that will transfer some amount of money from your account to another one. Also if you receive a call or SMS that tells you that your credit card is blocked due to malfunction of bank server and you can unlock it by calling a number and telling an operator its serial number and PIN code, never agree to do this, otherwise your card's serial number and PIN code will be stolen.

 

You may receive a call telling you that you have won a prize in a lottery organized by a radio station. To receive the prize, as the voice says, you have to buy your network operator's express payment card, or even several, scratch them and tell the person calling you their activation codes. Now try to guess what that person will do with your codes and decide whether you should do this or not.

If being told, in a call, SMS, email spam or otherwise, to call a four-digit number or send a message to such a number, do not proceed unless you really know what you are doing! All calls and messages directed to such numbers, except special network operator's support service numbers, are being charged at premium rates.

 

One variation of such mobile fraud happens when you receive an ICQ message from someone with a nick "ICQ administration" (sic!), but with an ordinary, long UIN, telling you that you have to "validate that you are really a human, not a robot" by sending an SMS to such a four-digit number. To tell whether this is fraud or not, just ask yourself: can genuine ICQ administration really have a long UIN?

Same applies to ordinary, long numbers in codes 803 and 809. These can be easily confused with toll-free 800 code numbers, but, unlike them, are being also charged at premium rates. Just read the number carefully to avoid such mistakes.
If in doubt, do not hesitate to call your network operator's support service and ask how much will it cost to call a specific number or to send a message to it.