Phone phreak

A phone phreak (phreak for short) is someone who displays most of the characteristics of a hacker, but also has a specific interest in the telephone system and the systems that support its operations. Additionally, most of the machines on the Internet, itself a piece of the Public Switched Telephone Network (PSTN), are linked together through dedicated, commercial phone lines. A talented phreak is a threat to not only the telephone system, but to the computer networks it supports.