It probably needs to be transmitted in parallel, out of band, rather than trying to integrate it into the existing phone system. That's how Google's Verified Calls thing they were touting a few years ago worked to give you context about a call by having the company placing the call relay data through Google and to an Android device's phone app with additional info like the reason for the call.

This won't work since Caller ID is too easy to spoof.

> The Federal Communications Commission requires use of the protocols by June 30, 2021

Well, then, looks like the problem was solved nearly three years ago!

This is what STIR/SHAKEN is supposed to do. Your phone and carrier in the US probably support it, but it’s not obvious. On iPhones there will be a little check mark under the number for inbound calls on your recent call list. This doesn’t carry over to things like voicemail however - where the check isn’t shown.

This model also doesn’t work for businesses that route all outgoing calls through one number, as that is essentially caller ID spoofing.

I'm neither from the US, nor an iOS user, I don't think I ever saw a checkmark when recieving a call.

The Google dialer does ask me whether unknown callers were businesses and try to ID businesses that enough people report