Bluntly-- I think these people are assh*les.
Having nothing better to do with one's time than think up 'pranks' on strangers (and I don't think these are pranks, these are invasive intrusions into other people's lives) is pretty sad and pathetic. And incredibly sociopathic, in my opinion. Or narcissistic, take your pick. (this does fall under the clinical explanation, too-- NO recognition of the feelings or needs of others, No recognition of the consequence of their actions, NO remorse for what's been done, just the desire to be the center of attention and 'in on it' no matter what the cost to the people affected.)
Yet, let's also put some of the accountability into the hands of those that listen to the show, cheer it on, and think these so-called pranks are awesome. Morons, too. Great if you are in high school, but if you can think for yourself, it's pretty appalling to target random strangers for a cheap,unimaginative laugh.