You're Canadian eh? Try this
http://www.crtc.gc.ca/ENG/dncl.htm
I put our number on this DNCL. Calls have dropped off. There are some exceptions to the rules however.
You can usually tell if it's a telmarketer by the ~1 second dead-air when you answer: I just hang up. An automated system dials the phone numbers so when you answer it detects this and connects you to a live person.
Or I let voice mail pick up. Or I simply tell them I'm not interested. Whatever mood I'm in. I've also asked them to hold while I put the phone down etc. as others have mentioned.