Aparently, being silly is the way to stop telemarketers:
1) You know, I'd really love to talk, but the Viagra is just starting to kick in.
2) I just finished stuffing my mother-in-law into a trash bag and am way behind schedule.
3) I'm sorry, I can't take this call, I'm too busy telemarketing a competing product.

this very well designed website will surely help.