Block Annoying Medicare and Medicaid Junk Calls

My grandmother has been receiving calls non-stop about medicaid and medicare products that she may be interested in signing up for free. It is unfortunate these companies target the elderly and most of the callers aren't even native speakers. Since government information is public record, they no doubt obtain her number through the Public Information Act. So how did I stop her from getting these constant harassing calls while still allowing calls from family and friends to go through? I simply set up a miniature PBX phone system. No internet is needed for this setup. She got to keep her existing phone number, cordless phones, and service. While I could have put her on an all VoIP (Voice over IP) solution, I opted against that since she may need to dial 911 and I would prefer that call to go...