i like to waste their time, if i'm not busy....
what i do is act interested, then say "oh damn, the kids are trying to kill eachother" then i put them on hold for a few minutes...if they are still there i apologize, and ask them a few questions....then i say "oh, hold on i need to get something" put them on hold again...after i have wasted their time as much as possible, i then tell them i am not interested, and never was....i just enjoyed wasting their time so they couldn't call anyone else and harass them....they sometimes wget mad and/or whine at me..."it's just a job..." so i tell them to get another one, that doesn't keep feeding the beast.
but i'm kinda bitchy like that....you should see what i do to door-to-door soul solicitors....