This works in many countries, since the signalling protocols historically assumed a trusted small set of participants, not unlike email – with similar consequences once those assumptions became less and less true.

I've worked a bit on the app which calls major telco provider directly. It was a basic web service call, and sender could be entered as anything. This is basic property of cellular networks, no more safety than say standard email.

It might have been the Ringworld

"Well?"Nessus began to pace the floor. "Many disqualify themselves by obvious bad luck. Of the rest, none seem to be available. When we call, they are out. When we call back, the phone computer gives us a bad connection. When we ask for any member of the Brandt family, every phone in South America rings. There have been complaints. It is very frustrating."

https://www.naneahoffman.com/the-blog/shelf-care-alien-archi...

Ringworld. https://sciencemeetsfiction.com/2021/06/20/ringworld-theory-...

    “When we call, they are out. When we call back, the phone computer gives us a bad connection. When we ask for any member of the Brandt family, every phone in South America rings.”

lets play a game HN, what would be the best alert to send?

mine would be something scifi, like "ALIENS HAVE LANDED" or "PLUTO DECLARES WAR"

At least it wasn't a crypto scam.

This implies that governments didn’t already have this ability, which appears to be largely untrue? To my understanding, many countries already had emergency messaging systems, and mobile integrations are just a way of modernizing them.

(It seems exceedingly good that the government can warn every civilian about natural disasters, etc.)

These aren't from Google or Apple, they're from the wireless providers: https://en.wikipedia.org/wiki/Cell_Broadcast