> The more you see the underpinnings of it, as I have, the more it looks like a bunch of 30-year-old bullshit held together with the technological equivalent of duct tape and twine.

This happens to every system eventually if it lives long enough.

My biggest takeaway from it is that many things standardized before a certain era are based entirely on two concepts of operations:

a) only a certain elite group of people or companies will be able to use it (in this case, PSTN operators)

b) total trust between all parties using it, so there's no need for provably-hardened cryptography.

both of which are now laughable in a modern network security threat environment.

In this case SS7 was just never designed with the concept that malicious third parties might get access to it, or that it would not be operated by RBOCs (regional bell operating companies), or the international equivalent thereof (national run telcos such as British Telecom, Telecom Italia, etc).