There is a way to sign up for a FREE service called nomorobo to stop these annoying robocalls. My problem is that my landline carrier, AT&T, currently doesn't support Nomorobo because they need to add the Simultaneous Ringing rejection capabilities to their service. I've called AT&T months ago, as the Nomorobo.com page suggested, to request they help stop spam calls with this, but they don't seem to care and have no solutions of their own that worked (yes I even paid extra for one of their products that was supped to help, of course... it didn't!
SO, I decided to use AT&T's call forwarding service to make AT&T understand the problem a little better and I suggest others do the same.
After I get a spam call I enter it into my "call forwarding list" (*63). The number I have dialed in for the call forwarding is: AT&T (Traditional Landline) Customer Service 1-800-288-2020 (make sure you use the number "one" in your entry).
I'm hoping if they start to get the same number of spam calls I get - they'll decide it's worth stopping the problem.