The trick to making these calls stop is to convince them that they are wasting their time and resources to call you. This is very difficult to do since the resources that they waste are small and the reward of scamming you out of your money is so great. I have found a way however. You must proceed until you get to a live person. Then tell that person in the most forceful, obscene fashion that you can that they should go engage in intercourse with themselves and then call you back to report the results. This conveys the idea that subsequent calls will not be productive and they remove your number from the list more certainly than any other way that I have found. It also is very good for relieving the frustration that they have caused you to feel.
Perversely, this is also what is best for them since it prevents them from wasting time trying to wheedle you into changing your mind.
Try it, you'll like it.
Feel free to cut and paste this advice on similar sites!
I have gotten both 206 and 306 calls and just decline them. One time on an epicode of "Becker" I saw Ted Danson answer a telemarketer and set off a blow horn into the receiver...still makes me laugh....
Note to people who fuss about the Do Not Call list:
These folks are scammers, so they don't give two bits about some laws regarding who they can call. They operate offshore, so they're pretty much beyond the reach of US law anyway.
The best defense is to not answer calls you don't recognize, and forums like this.