tone filter

require through legislation that people making robocalls preceed their recorded message with digital tons indicating an identifying number which they obtain from the FCC. Receiving phones can be equipped with electronic filters which listen for the tones and can hang-up if set to hang up. Phones without filters answered by humans could manually hangup on calls upon hearing the tones or if a robocall comes in without tones a keypad combination could hangup and trace the call with info going to the FCC.