Ever work telemarketing? I did, only for a couple weeks though, and I couldn't stand it. Let me just say that the other end of the line is much worse, and next time you want to tell them to put you on the do not call list just do so. Basically the job consists of calling up people that don't want to be called, and have them be rude to you even though you dislike it as much as they do (if not more). One less person being rude and calmly telling them to never call back just makes their day that tiny bit better.
Keep in mind this is just my take on it...there may be some sick freak out there who actually enjoys the job, but I never met a single one.