The Telephone Butler does more than just reject robocallers: The butler puts the consumer back in control of their telephone service. Implementing the butler itself is just a simple matter of a software agent running in 'the cloud' using spam filtering type techniques. The hard part is providing reliable data for the butler to work with and this proposal shows how to do that.
In particular the two major problems are getting reports of robocalls from consumers via the horrible affordances of current generation smart phones and establishing a caller-authentication scheme. The first can be addressed through a speech recognition scheme now but a smart handset would be better. The second requires deployment of a PKI which done using the full PKIX type approach would cost too much and take too long. Fortunately we can take some shortcuts resulting in a 'scruffy PKI' similar to the DKIM scheme used to mitigate email spam to create an interim solution that we can replace as needed.