I have just been told of a telephone scam currently doing the rounds here in Cyprus.
It concerns mobile (cell) phones. If you receive a call from someone claiming to be an engineer, and they ask you to type #90 into your phone's keypad as a test, DON'T DO IT! They can then access your sim card, and make as many calls as they want.
I don't pretend to understand how this scam is possible, but I pass on the warning in good faith.