Phreaking is a slang term for the action of making a telephone system do something that it normally should not allow. It is an illegal activity, but one formerly pursued by a large number of computer and electronics hobbyists out of curiosity. Other reasons why many people attempted (or succeeded in) phone phreaking during the 1960s and 1970s included the (then) very high cost of long-distance telephone service, and a desire to rebel against the AT&T telephone monopoly.
A phreak or phreaker is a person who engages in the act of manipulating phones in this way. The tools of the phone phreak are electronic devices known as boxes, originally the blue box, but later the black box, red box, beige box and clear box etc.
Most of the techniques formerly used in phreaking are no longer effective due to changes in the telephone system. Some of these changes were evolutionary, and some were designed specifically to disallow such access. Moreover, the cost of telephone calls has diminished to the point where few would find it worthwhile to engage in toll fraud; and there are numerous competing providers of telephone service (except for most wired local service which remains controlled by regional Bell operating companies—remnants of the former AT&T monopoly).