Spammers have currently defeated SHAKEN/STIR. A signed call is more likely to be a robocall than not a robocall. This is thanks to shady phone companies that will sign calls for anyone or intentionally cater to scammers. https://transnexus.com/blog/2022/shaken-statistics-september... This is like when DKIM was first being deployed spammers adopted it first.
It significantly increases their costs though. As in the parent ruling here, a shady phone vendor that doesn't take steps to prevent spammers they will no longer be able to route calls to the US.
