Personally I feel no obligation to be polite to telemarketers. It makes them feel wanted, and that's a bad thing.

I feel slightly sympathetic to the telemarketer drones themselves, on the basis that it's probably an awful job and they'd be doing something else if they had any choice. The really responsible people were the ones who decided to hire a telemarketing department. I'd feel no compunction about, for example, calling those people at home and annoying them constantly; it'd absolutely serve them right.

(One could argue that the drones still have some moral responsibility, in the same sense that conscripted soldiers do; just because their alternative option was extremely personally unpleasant - bankruptcy or jail respectively - doesn't mean there wasn't something they could have chosen to do instead of making people's lives worse for a living. But it seems to me that their moral responsibility is significantly diminished at the very least.)

So usually I'm not rude to them unless they persist beyond the bounds of reason, for example if I say I'm not interested and they try to tell me yes I am. ("Excuse me, which one of us is me?")

My favourite trick for getting rid of telemarketers is to say "I'm in the middle of cooking dinner, you'll need to take less than thirty seconds, I'm not kidding". They invariably say they'll call back another time, and invariably don't, because (just like any other spammer) it's more profitable for them to try a fresh target than to retry after a temporary failure.

When I used to have a landline, I would just say "Hang on, I'll go get my mum", and then leave the phone on the side. They'd generally gone by the time I came back to hang it up an hour or so later :)

Admittedly this approach doesn't work so well with mobiles, but other than the end-of-contract upgrade offers, I've never had any telesales calls on my mobile.

Forgot to mention, the 'leave phone on side' approach being chosen for its 'tar pit' like qualities - not only did it improve the quality of my life by ending the call immediately (from my point of view), but it also improved the quality of life of anyone the telesales person didn't manage to call that day due to wasting their time waiting for my mum to pick up :)

Ah, yes; along the same lines as telling the canvasser for your party to go away immediately but inviting their opponents in for a cup of tea and a nice long argument. Except that in this case it doesn't cost you any of your own time either :-)

They have a lessened responsability, but not enough to get them off the hook. Mind, I don't tell them to piss off and die, I just say (very very quickly) 'I'm not interested thank you. Goodbye.' and put the phone down. But they're never going to get me to listen to them after they've said 'I wonder if you're interested in foo.' My view is that I'm not a moron, and that if I really wanted foo, my first port of call would be the internet, or failing that, yellow pages. Couldn't telesales drones have taken their excellent phone manner and persistence to, say, customer queries instead? That way they might be useful.

I suppose we should really shoot all the consumers who're sufficiently daft to respond positively to telemarketers. 'Yes, now you mention it, my life has a significant hole I'd never noticed before, which absolutely needs filling with a new patio. Thank you for making my life a financially poorer place."