UK SIM not working in Australia

Just letting People know that Smarty indicated to me that it was an Iphone issue (PLEASE, this is garbage).  My iphone passes the Telstra test (the main Telco provider in Australia).  It has not been black listed since the 3G switch off.  I have gone down the track of purchasing dumb phone which has all the current required capabilities for Australia just to prove it is not an Iphone issue (which Smarty have indicated they are awaiting a software update in March). 

If you scour the internet you will see that people from the UAE, Singapore, Thailand, etc are all unable to connect in the main.  The UAE website discussion boards were very complex and hinted at issues with 'agreements by your provider (Smarty)' with the Aussie Telcos to allow or pay for the Volte service.  I struggled to follow but it appeared to be if you had a Post Paid Service for Data you were ok.  So I am not blaming anyone but as it stands there does not appear to be a clear list of any Telco service providers in the UK that provide a roaming service that could be connected to in Australia. 

I understand the first hurdle is your handset, but if you pass that hurdle you are still left with the lovely SOS message.  If WIFI calling appears at the top of your screen it might be that you have won the lottery.

As to those people suggesting purchasing alternative local sims, give us some credit.  Most of us have done that.  Great cheap sims work in my Iphone SE 2022 (purchased in the UK - used Coles (Telstra and Amaysim - Optus).  The problem is the 2FA (who designed this hell on earth).  One financial institution said they could change to an alternate UK number (after they send a form to my UK address).  Great as a single person with no family or friends that could forward that to me in Australia - not an option.  My bank was as useless as they come (swore only a UK number can be updated to another UK number).  They verified me using telephone banking pin and suggested using a 'fax' service (please heaven forbid I need a subscription service for that).  Eventually they realised that I have been verified for phone banking and took verbal instructions.  So please don't make fun by suggesting Esim's etc and local alternatives.  This hell which modern technology has created which means we are identified by our phone number (remember we are verified by a piece of kit - you the person using it are NOT verified by this).  As Australian I can't find someone who is even willing to sort this mess out.  I can't update any UK apps that are sending codes via SMS - having even lost access to my phone banking APP as it needs to be re-registered using 2FA.  I can't approve any credit/debit transactions as they are approved via the banking App.

Is there anyone who has managed to use their UK sim in Australia (phone handset is not relevant at this stage).  You can buy a $40 dumb phone to put the Sim if you are caught by the blocked IMI handsets.  My brother has terminal cancer and I would like to extend my stay but I can't keep trying to get into important transactions via a series of ignorant banking employees etc.   2FA is great if your institution allows authenticator apps but many processes do not.  

If anyone has relatives/friends etc. that are using a UK number in Australia and would share their set up I would greatly appreciate.   At this stage Smarty are just waiting for Apple to do a software update which quite frankly I doubt will do anything.   It really does appear to do with Telco agreements as it is impacting so many different 'plans' worldwide.  I

f you port your number do you need to be able to get SMS codes to do so.  

Sorry rant over

List of working UK SIMs would be appreciated (yes, I have roaming credit etc and like others have used my existing SIM for several months before 3G switch off).  I have tried to view the community notice boards of other UK providers, and it is not clear that any are working as intended.  Volte agreements appear to be the issue?

Thanks