Yeah, SS7 was not really designed for the scenarios it now finds itself in (hell, I remember my dad talking to me about it back in the 80's). It's amazing how well it works, but that's exactly the context where one expects to find security vulnerabilities in spades.
https://www.economist.com/science-and-technology/2024/05/17/...
(Accompanying editorial: https://www.economist.com/leaders/2024/05/23/hacking-phones-...)