alt Hacker NewsThe problem is that it's a network. The hard part of networking isn't the technology - it's the other people. And short of a government regulation or a monopoly, they'll never all agree.
STIR/SHAKEN has an exception for calls passing through TDM trunks, which don't support it. This created a small industry for passing spam calls through TDM trunks. Such calls can trivially have their caller ID spoofed.
> short of a government regulation or a monopoly,
Phone companies used to be monopolies, in Europe they were owned by the government as a public service. But when they become profitable politicians betrayed their citizens and sold them. Nowadays, phone companies are a source of scams, spam and everything wrong with big corporations. And all that profits are now private instead of helping to fund the country.