Phreaking is the act of playing with and exploring the phone network and other systems connected to it in the spirit of fun and knowledge.
It ties in pretty heavily to the values of computer hackers, and while I consider myself a part of both communities (though somewhat disconnected from the mainstream hacker scene), that isn't really a requirement.
I evidently consider myself a Phone Phreak, meaning I engage in these activities and probably have a dartboard with my face on it at AT&T's HQ in Dallas.