Alan sez, “Nomorobo recently won the FTC’s contest for best anti-robocall invention. It uses a feature of the phone system that’s already mostly in place which lets the Nomorobo device get the call at the same time as you do, checks the calling number against certain spam signatures (e.g. calling blocks of numbers sequentially) and auto-disconnects the robocaller before your phone even can ring.
Anyone who claims you can’t do interesting things purely with phone call metadata has not thought about the problem long enough.”