I worked in a call centre for almost a year. Basically what I did is switch people from OLD (more expensive) plans to newer plans with better rates. People tried the most obnoxious things, but first of all we were able to hang up after xx amount of seconds if there was no response, or we were put on hold for more than xx amount of time. And secondly, in my situation people, once they stopped being rude were actually thanking ME for calling at the end. And yes all of us are people too, and no I don't live in India, or another far off country.
For you folks out there who are the rude people that have no respect for someone else here's what you do:
There is such a thing as a "Do Not Call" list, and like someone mentioned, it has nothing to do with your number being listed or not. SO before you swear\put someone on hold for hours here's what you tell them.. First listen to what they're calling about, because who knows what it is they're offering, heck I was offering FREE service for 3 months of high def. cable at one point, NO strings attached.. Then if you're still not interested, say "PLEASE put this number on the Do Not Call list". They LEGALLY have to put you on that list. BUT what usually happens is your number gets recycled through the call centre's list for a week or two, then finally it kicks you out. (but your number only stays on that list for that company for 3 years or something like that..dumb laws.. in my opinion it should be FOREVER lol) So it is possible that you still get a call within that time frame. The worst thing you can do (and they'll call even more) is tell them the decision maker of the household isn't available, not answer, or hang up on them.
Just my 2 cents, and I've NEVER had a repeat telemarketer\telesales call.