A term or two is in order. Hacking, despite the common misconception promoted by the media that it is illegal or somehow wrong, is not. Hacking is a mindset applied to solving problems. WHY and HOW it works. Hacking is a lot of things.
Some people hack for good reasons, others for the wrong reasons.
They might call themselves hackers, but they sure don't act it. Phreaking is a telecom type of hacking. For the most part, illegal, since often the object is to gain access to telecom services without paying for them. This isn't to say that all phreaking is illegal or wrong though - most of the people who deal with your telephone systems do some amount of phreaking in the everyday application of their jobs. There's a big one.