Damn, it might be worth the $30 just for fucking with the spammer.I pay for an app called RoboKiller.
There is a 7-day free trial and then I believe $30 for a year subscription.
It does a GREAT job of identifying and blocking spam calls.
However, the best part is the auto-answer that has a funny selection of pre-recordings that talk to the spammer, making him think it's you. So, basically, the phone app answers the phone and keeps the spammer talking before they realize they are speaking with a recording. Then, you get to hear the entire transaction afterward for a good laugh.
I can't put this thing properly into works. Just go to the app store and download it. Try it for a week and see if you like it. I think you will.