You're correct. You can see them both in the source code here:

https://github.com/alphagov/notifications-api/tree/master/ap...

Similar to Japan, the US has https://www.fcc.gov/consumers/guides/wireless-emergency-aler....

I think this is just GSM Cell Broadcast [1].

It seems strange that it would be complicated or expensive to set up. I've used cheap, aimed-at-tourist SIMs in developing countries where cell broadcast was used to send news and adverts, which is very annoying.

[1] https://en.wikipedia.org/wiki/Cell_Broadcast

ya this has rapidly the last few years become the standard in Canada. I think the government mandated all the major providers enable it/support it and they did some tests and people initially freaked out (phone alerts at odd hours alarmed people) but then 'for the greater good' people got used to it (and learning to use volume and DND settings). Main use is timely emergency alerts for missing children. Used to be done across television and radio (still is I suppose, not sure, less people have cable television and who's got the radio on). Proven effective on a number of occasions too. And especially in recent coronavirus times it's been used to send more general notices for the first time insisting people stay home/self-isolate and warning travellers returning home from abroad to quarantine for 14 days.