According to the BBC:
US Congresswoman Ileana Ros-Lehtinen thought she was being hoaxed when a man who sounded a lot like Barack Obama called her – so she hung up on him. In fact, the man at the other end of the line was indeed President-elect Obama himself. It took two further phone-calls before Ms Ros-Lehtinen was convinced that the telephone call was genuine.
You’d have to feel a little silly wouldn’t you?