Customers suddenly find their new phones can't make calls or send texts

This isn't regulatory. It's Optus deciding that if they didn't sell the handset or its foreign bought it is will be blocked. Because of reasons...
And don't ask questions because software is hard, and telecom is too technical for the plebs.
It's nothing but a blatant cash grab hidden in a thin veneer of technical babble because it's tough for modern journalists to question engineering.
- Just days ahead of the shutdown, Australia's media regulator ACMA finalised a new "direction" (basically a rule) that meant telecom companies had to refuse service to all phones that relied on 3G for making emergency calls.
  The idea was to prevent people from mistakenly believing that phones were fully working, only to realise they were unable to make emergency calls when the crucial moment came.
  Australians with older 4G phones may also be caught out because of the way the phones are configured.
  It is up to the telcos to work out which phones are affected, notify the owners, block their phones, and help make other arrangements such as low- or no-cost replacement phones.
  However, as Telstra and Optus noted during a Senate inquiry into the shutdown, telecom companies are unable to tell which individual devices suffer from this problem unless have they sold them.
  I'm not saying it's not partly on the providers, but validating that a bunch of obscure phones that aren't sold in your country meet new regulatory requirements is not as easy as you're making it out to be.
  
  That's the reason why every other fucking country still has either 3G or 2G activated. 4G is just a shitshow for making calls.
  
  So to let people know that they won't have emergency service during an emergency, they prevent them from having ANY service now (24-hour notice). Even if telecom companies behaved perfectly (which they wouldn't) the initial idea was already a problem.
  
  It's not a bunch of a large number. It is a set number of phones from well known providers from a few countries.
  Basically no one wanted to pay for one Business Analyst to read documentation and make phone calls to providers. For a program that has years and millions in it.
  Or worse, cause it is out of scope
  Or the worst, so they could sell the "buy from the provider" bullshit
  
  They also refused to use the standard voice over LTE and refuse to let any thing that they didn't sell try to connect to their voice over LTE even if it's compatible. Leaving restricted Apple from enabling voice over LTE for iPhones not from Australia even though it's just a software update that you need that doesn't run on the firmware level.
  
  If only those affected could call for an appointment to swap to those low or no cost phones.
- Are Japan radio frequencies the same as Australia?
  
  Sites like frequencycheck.com let you find out based on country, carrier or device
  
  If by radio you mean the music device, no. My jap import cannot pick up aus stations. If you mean radio frequencies for phones and others, hopefully someone else has the answer haha.

- It doesn’t seem wise to make your cell network work all that differently from the rest of the world when cell phones are supposed to work seamlessly across borders.
  This is/was the USA with their very different system.
- This is the USA. Since when is the US part of the rest of the world?
  Seems most the world wants to distance themselves from us. Except for some shithole countries.

This is a safety issue — a matter of life and death — so if there is any doubt, we are compelled by law to block to protect customers,
What is that mental gymnastics? They are blocking customers in life and death situations from making emergency calls.

They should have built a solution where the phones that haven't been tested get cut off, but get an SMS telling them to activate the phone, call SOS once. For the first SOS call, they intercept it, check that the phone was able to make the call, then unblock the phone, and after that, allow SOS calls as normal.
That would require "actually doing work" though.

The telecoms are using bad-faith interpretation of the new rules to require their customers to buy (often identical) phones directly from them. This is a corporate money-grab and it needs to be aggressively addressed.

lol fuck every tourist in the ass sideways I guess.

Guessing some of the commenters have never dealt with Telstra here in Australia - it’s already reported that these telcos just flat out never tested any phone that they haven’t sold - phones that up until now were actually working perfectly fine (and even have the same model handset being sold by Telstra/Optus/Vodaphone etc) suddenly disconnected.
It is purely laziness on the part of Telstra and the rest of them and they are using it as an excuse to get people to buy their handsets instead - have not seen one of the “offers” of zero cost replacements either…..
Telstra are just corporate scum and this could have been handled a whole lot better but then again you only have to look at the shitfight that we have here called the NBN - a national government funded internet network that the telcos will charge you more than the rest of the developed world to access and nowhere near the speeds, level or service or quality as seen in the rest of the world…..
Nobody here in Australia is really surprised this was a massive cock up and anyone who is mustn’t have ever heard of Telstra then…..

I actually may have this problem eventually in the United States as well, because I'm running a OnePlus Nord N200 with lineage OS, and it does not seem to be capable of voice over LTE while running lineage OS, but will work fine with voice over LTE using the stock ROM, which I refuse to use. Right now I either have to be within range of Wi-Fi or if I place a call my phone falls back to the 2G network in order to place the call and then flips back to 5G when the call ends.
Edit: on T-Mobile. I do not believe it will work on AT&T at all, and I have not tested with Verizon, so I'm not sure.
Edit 2: I think voice over LTE could be made to work properly because I've seen other lineage OS devices that work fine with it. So it must be something with this specific ROM.

if they were bought overseas or via international resellers.
Classic blunder. Don't forget to check mobile bands of radios you buy kids!
- It's not just the bands. You could have all of the needed bands and still be blocked (and you could me missing one and just get a warning).
  
  Can confirm. My phone got kicked off when they started sunsetting 3G. They called me (on said phone with no service lol) and said I needed a new phone. I said "no I don't, put me back on the network". We went back and forth, then they forwarded me to the tech department
  The tech says "you need a new phone". I said "no I don't, I have all but one of the new bands and others with my phone have already gone through this process with you guys". He said "you can't believe everything you read online", I said "be that as it may, I looked at the specs for both my phone and your network, and it meets the requirements"
  He starts telling me there's nothing he can do on his end, I say he just has to find an override to stop blocking my phone. He says he doesn't have any options like that, I promise him it's there
  After getting tired of going in circles, I say if he doesn't know how to do it he needs to ask someone or pass me to a higher tier. Surprise surprise, my phone instantly shows bars and he tries to gloss over the whole thing
  
  This exactly, as long as your phone has at least one frequency band of the provider, then it will at least connect to their network and allow you to access data. Calling seems to be a whole different thing, though, because it requires something with IMS.

Makes me feel slightly better to know I’m not the only one living in a country (United States) where foreign bought phones are a hit or miss on the networks. wish they could create a better system though.

"We gotta shut down 3G as fast as possible so we can get black spot grant money and then use that money to rebuy the spectrum space at the next auction."
-Telstra