Reverse Phone Lookup

My friend, a fellow mom has been complaining that she has been receiving a number of prank calls several times a week. It's weird because most of the time, she hears a child's voice at the other end of the line. A very bored child must be calling her. She is thinking of changing her land line number. A reverse phone lookup feature would be great to trace any unidentified calls. You can always find out Who's Number Is This.