A typical case of this scam is a one where someone opens a premium rate number at local telecom operator and starts sending SMS messages to random mobile phone numbers. A typical message contains some urgent message and instructions to call the number listed in the message.
If a person calls this number he will be connected to premium rate number which will contain recording intended to keep the user on the phone as long as possible. As the number where the user called is a premium rate number, he or she will pay for each minute spent connected to that number.
If you get an SMS message asking for you to call unknown number, either ignore the message, or if you are interested use the operators directory service to find out to whom that extension belongs. But do not call the number directly.
If you get email warning about such scam, please ignore the email and do not pass it on. If you want verification about the warning, please contact your local telecom operator.
-UK June-July 2001 Scamsters sent SMS messages to random people containg following message 'Please call me on 09011 500065 Urgent"' If a person called this number he will be connected to premium rate which played busy tone to fool the caller that the line was busy. The number charged £1.50 per call.
This case is no longer a threat since the extension in question has been closed.