This is taken from my own website and I came up with them all on my own.
When You Don't Feel Like Tormenting Them Must Anyways
Don't say anything, just lay the phone down and walk away letting them go through their spiel. I imagine this one must be fairly annoying to them. This works with all types of telemarketers.
Bark at them. Repeatedly. I've actually gotten telemarketers to bark back before.
For ones that start out by saying that they would like to tell or inform you of something, tell them thanks for letting you know and hang up.
When You Have Some Time To Kill and Feel Like Having Some Fun
This is one that I've done many many times and never get tired of their reactions. It will by default only work with people wanting you to switch your phone service. When they start to go into their bit to get you to switch to their service tell them you don't have a phone. Obviously this is a lie because you are talking on the phone. Say it and everything after as calmly as posible, much in the same way you say the sky is blue. They will try to argue with you. When they ask if you are the owner of this phone number answer them by asking why would you need a phone number if you don't have a phone. When they ask how you are talking to them say you don't know since they are the ones that contacted you and you don't have a phone. One guy said that he hit the buttons on his phone and then "these voices start coming out of it." He didn't like it when I asked him if he hears voices often and politely suggested he talk to someone for it. Another important thing with this one is to not hang up on them no matter what. I've had them put me on hold thinking I would hang up. Most telemarketers are told to never hang up on a customer. That way, do you not only get to bug them, you get them in trouble with their bosses. The best time I ever used this one I had the guy on the phone for almost half an hour. I would repeatedly argue with him that I don't have a phone and he would put me on hold thinking I would hang up. He was wrong. I was having fun with him. Why would I hang up?
Some companies will call and say that their records show that you have been preapproved for whatever it is that they're selling. Tell them you checked their records and you haven't been preapproved. Whine that you really do wish that you were approved because you want what they're selling quite badly but hey, the records say what they say and you can't argue with them. If you have a keyboard handy make some typing sounds and tell them that you're checking right then. Suggest that the telemarketer must have an old copy of the records and they should get today's version. Especially fun if they aren't very computer literate.
When credit card companies call tell them that you don't believe in money and only barter with farm animals. After telling one lady that she tried to convince me that I needed their credit card anyways by talking about how you can pay over the internet (oooooo, wow, the Internet!). She didn't stay on the line much longer when I asked exactly how I would send a sheep over the phone to my ISP.
Act very interested in what they are trying to sell you. Tell them that you've got someone on the other line and that you need to end the other conversation before you can talk about their wondrous offer. Don't have someone on the other line or like me and not even have call waiting? That doesn't matter. Just make some beeping sound (hitting one of the number keys works) and act like you're talking to your friend on the other line. Tell "your friend" that you've "got another one of those idiot telemarketers on the other line. This one really sounds like a bigger idiot than the rest of them" and that you've got to let them go so you can go and really have some fun with them. Telemarketers don't like it when you do that. Its almost as annoying as someone calling you at home at an inconvenient time trying to sell you stuff.
Back down the bullies to the back of the bus
Its time for them to be scared of us