It's the law.

• GIF

Instead of creating some kind of device that the common phone user would have to learn how to use, just make the companies that send the Robo Calls buy a license and mark there numbers with something no normal person would have. For example **2 or #*6 and then the rest of the phone number. This could be a federal law as well, creating a from of tax that could help to fund many local or federal programs. If the call center refuses to comply with the new law, just shut them down.