Hehe, I came across this just 10 mins ago:
1. When they ask "How are you today?" Tell them! "I'm so glad you
asked because no one these days seems to care, and I have all these
problems; my arthritis is acting up, my eyelashes are sore, my dog
just died..."
2. If they say they're John Doe from XYZ Company, ask them to spell
their name. Then ask them to spell the company name. Then ask them
where it is located. Continue asking them personal questions or
questions about their company for as long as necessary.
3. Cry out in surprise, "Judy! Is that you? Oh my God! Judy, how
have you been?" Hopefully, this will give Judy a few brief moments
of pause as she tries to figure out where the hell she could know
you from.
4. If MCI calls trying to get you to sign up for the Family and
Friends plan, reply, in as SINISTER a voice as you can, "I don't
have any friends... would you be my friend?"
5. If they want to loan you money, tell them you just filed for
bankruptcy and you could sure use some money.
6. Tell the telemarketer you are busy at the moment and ask them if
they will give you their HOME phone number so you can call them
back. When the telemarketer explains that they cannot give out
their HOME number, you say "I guess you don't want anyone bothering
you at home, right?" The telemarketer will agree and you say, "Now
you know how I feel!"
7. Insist that the caller is really your buddy Leon, playing a
joke. "Come on Leon, cut it out! Seriously, Leon, how's ya
been?"
8. Tell them to talk V-E-R-Y V-E-R-Y S-L-O-W-L-Y, because you want
to write down EVERY WORD. 
