We switched phone carriers about 6 months ago and got a product they call "Terminating Call Manager" for a one-time $30 charge. We've had exactly zero telemarketing calls since then. In its own way, it's kinda like dying and going to heaven.
While investigating call blockers about a year ago I found one called NOMOROBO. Seems the FCC had a contest for coming up with a call blocking device and this guy won. The Do Not Call list is unfortunately a joke and not worth the effort our government put into it. Like others here, they even spoofed our own number, which forced me to block it; darnit, I hate it when I can't call myself. *grrr* Oh, and NOMOROBO is free for consumers but your phone company has to support it and as I recall it only worked on landlines. Just Google it and there will be tons of information.