Comparing PSTN to instant messaging walled gardens is interesting, but I’d argue the real parallel is email: a federated, open standard that also suffers from spam and abuse, yet still manages to limp along thanks to heavy filtering and layered trust systems. The PSTN never evolved those trust layers; instead, it relied on scarcity (call cost, geographic constraints) to keep abuse in check. Once those costs collapsed, the trust model collapsed with them.
As for the FCC, sure, they can try to incentivize carriers. But the fact that we need constant regulatory intervention just to keep basic trust afloat suggests the system is no longer structurally sound. Band-aids like STIR/SHAKEN prove the point: we’re bolting authentication onto a protocol that never envisioned it. That might extend its life a little, but it doesn’t make the foundation any less fragile.
So the question isn’t whether the PSTN once had value (it did, massively), but whether preserving it now delivers more value than the cost of propping it up. If a good chunk of people already treat unknown calls as spam until proven otherwise, then the social contract around the PSTN has already been broken.