http://www.research.ibm.com/journal/sj/414/forum.pdf describes Scott Fahlman's vision to limit unwanted email and phone calls. It's an interesting system that deserves consideration. I find it a compelling suggestion because at the same time that it protects me from really junky spam, it protects the rights of a business to attempt to solicit me.
They just have to be willing to pay me enough.
Let me know what you think.