Phreak
A phreak or phone phreak is a term used to describe an individual who illegally breaks into the telephone system to make free calls or to tap another phone. In an attempt to help identify phreakers in 1964 AT&T started monitoring phone calls and is believed to be the first known time phone calls were monitored by a company. The phone monitoring was a success and led to several successful convictions and a drop in phreaking.
Also see: 2600, Blue box, Hacker, Security definitions