while out of 100 who say "Don't bother me" there's 1, maybe 2 that will actually buy something when they hear "that incredible offer'.
Telemarketers live on that 1%.
The easist solution to this - charge more for business lines. (Or charge per phone call.) Make it uneconomical to call people and this business model disappears.
PS: Of course, the other solution is to provide Telemarkets an example of [link|http://www.the-dma.org/aboutdma/contactthedma.shtml|OUR FREE SPEECH].