[walrus01]

If I have full control of a DID, implementing callback isn't hard. That would be a bandaid type solution built on top of the existing phone network, however. Fixing ss7 at a systemic level so that all call routing in and outbound is verifiable, CID spoofing is impossible, is what is nigh impossible.

[supertrope]

Are there any proposed replacements? Even SIP has vulnerabilities, foot gun features, and fundamental design problems like use of MD5 digest, NAT intolerance, and vendor and device specific bugs.