Collaborative filtering is better than law IMO.

My phone company shipped a phone app in the app-stores that you're supposed to use in replacement of the default phone app. It comes equipped with collaborative filtering to weed out robocalls: when one rings your phone, the phone app displays it as such as well as the number of people who have reported it.

I used to have one robocall a day, but not anymore. It looks like this simple technology has made robocallers give up.