I've posted about a similar situation in sg, not as extreme, but not far off.
@gaoqikai has posted about the aus situation too.
here's a link to a video summary:
solution from the video: when you land, buy a new phone from from the telco you intend to roam with or buy a local SIM and that's not guaranteed to work. Used phones probably won't work.
I have read reddit posts that in usa, AT&T blocked phones based on models, but would white list the particular phone's IMEI on appeal. no such mechanism here - consumers here are price takers.
I won't be surprised if telcos here follow suit and limit support to only models they sell.
Already, some phones (models, or even brands) that work on one telco here, won't work on another telco. You have to do more research before porting out. Heck, you need to do a lot more research and future prediction before buying a phone (will it be supported 1-2 years down the road?) . Or just buy a flagship Samsung or Apple......
the video also mentions withdrawing support in future. it's already happened here. At least one telco (MNO) has shrunk their supported list from last year.
There is no appeal mechanism. But they have a shiny new phone they want to sell to you!!!!!
It is a "business friendly" environment here, after all.
Ending on a slightly positive note. Most of my calls in the last few years, are via VOIP apps, so I'm fine as long as there is a data connection. Normal incoming phone calls are mostly scammers, so lack of VoLTE calling capability is no big deal, in fact, the absence of scam calls is actually quite refreshing.
of course, if i still want to receive "normal" voice calls, i could switch to Simba and use their voice app, but I'll have to put up with their, uh, fantastic network coverage and speed.