To talk about trolling we need to first try to define it. Rather than merely cite authority, I think we can see for ourselves that the word refers to either the verb or the noun. Personally, I believe the word takes its root from the fishing verb of trolling, that is, moving the bait slowly through the water or pulling it behind a moving boat in an attempt to get strikes. Interestingly, the noun form does not damage the definition: the dungeon figure of something hard to kill that regenerates its damage seems to apply to our internet trolls; so does the fairytale image of some ugly monster who blocks a bridge or gate and prevents good people from going into, or functioning within, the community. Instead, the noun seems to be descriptive of those who are involved with the activity described by the verb.
There are several media on which I have witnessed trolling. It is hard to know where to begin in describing it online, and almost impossible to compile a complete anthology of the most popular trolls -- so I will let those commenting help me on that section.
On Phil's show, we hear a variety of fake guests: racists, sexists, rich 'guests' who feel they are better than the average person, the lawsuit-happy, and experts who are really idiots in disguise. Given that the callers are real (which is not at all clear to me), the joke is on them when they call to complain about the guest's views. The 'guest', really Phil, almost always moves the argument to a personal issue with the caller rather than the social issue that the caller wanted to argue about. We see a lot of this online, as well. The goal is to infuriate the caller/victim until they start to yell or hang up. Since the medium of radio allows you to hear people's voices and guess their emotional state of mind, this is funnier than the online version where threads degenerate into massess of he said and she said, >>>>>, >>>>>>, and name calling where you can no longer tell who is calling whom what.
A similar phenomenon occurred on the Magic Mountain 2m amateur radio repeater when I lived in Southern California several years ago. Basically, people disobeyed rules like "no obscenity", and "no interfering with others' transmissions". These are not merely good ideas, they are FCC regs backed up by $10,000 fines. The sound effects that certain people transmitted to interfere with others' transmissions were often quite fancy and required some technical knowledge to produce. This was trolling in the classic sense, to attract attention rather than merely scoff at the rules. It attracted both the self-proclaimed ham policemen as well as a number of lurkers who might occaisonally become participants. Unfortunately, a few of the repeat violators received the $10,000 fines and one even bought a little prison time. It is not simply the internet that has no sense of humor -- any large community will include those who insist that strict rules be followed to the letter, and harsh penalities be delivered to the violators.
A bit of history may be in order. Amateur radio is not supposed to be like CB or the internet, but rather is a community of technical people who passed tests to obtain their licenses and who are supposed to obey certain rules. There is a whole tier of licenses, from novice to extra class (though it was recently shrunk by the elimination of "Technician" and "Advanced" class), which tends to instill a sense of hierarchy in the community. Usually, these communities are well ordered and the higher classes are quite willing to remind the younger hams about the rules. In extreme circumstances, the owners of the repeaters (radios placed atop mountains to repeat transmissions and make possible communities based on line-of-sight VHF and UHF technology) can just turn them off. This is akin to Rusty moderating kuro5hin by threatening to turn off the server when annoying posts or comments started to appear, and then turn it back on later -- except that the medium is audio, rather than text.
In truth, anyone can buy a radio -- you need not show your license. It is actually quite difficult to track down those who violate the rules, and so the ham radio medium allows a certain amount of anonymity -- especially for those who break the rules and do not give a call sign.
Although it would seem that the ease of attaining anonymity and a low cost of discovery are primary factors in determining the amount of trolling, Phil's show makes it clear that anonymity is not necessary and the hams make it clear that people will troll even if the potential cost of discovery is very high. Perhaps there is something else involved.