I just stumbled upon this service recently:
http://www.jollyrogertelco.com/
Basically, when you get a scam/spam/telemarketer call, you can waste their time by texting that service, it will call you, and you can conference the two calls. Then an automated response system will converse with the nuisance caller and waste their time.
It doesn't work with all service providers, unfortunately--not all of them can merge two incoming calls. It's still a neat idea if you are frustrated with nuisance calls.