Sokha Call Filter (SCF) or (aka, ZapIt) is a response to the FTC Robocall Challenge of Fall 2012. SCF is based on CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart).
SCF utilizes existing equipment that most people already own. There would be no changes to VoIP gateways, phone switches or phone companies. Therefore, the solution can be deployed rapidly and affordably.