Phone calls now produce JSON Web Tokens that identify users with cryptographic signatures. This was codified around 2018 by the IETF, SIP Forum, and ATIS.

So the public phone system now supports it, but the problem is that not all providers support it yet, which fundamentally weakens the system. Of course, you can’t just add a new “protocol version” to an over-100 year old phone system with zero time to do a migration.*

But now that it’s been a few years, we are reaching a point where, at least for the US, the FCC wants to ban any provider who hasn’t added support.

*simplification