I am using Kogan which although has great deals on data, is pretty expensive for roaming. $12 for 500MB and 100 minutes and 100 texts for 3 days so I decided to pass on that and purchased an eSIM for data only resigning myself to if people call me, they will get VM and if a text, then silence.
Surprised to receive a text from DHL telling me when a package I was expecting was about to arrive. So checked with a friend and asked them to send me a hello SMS which I got. So it seems while I have no roaming turned on, I can get SMS and I can call back using another means if needed.
I did note when I arrived in the overseas country I did get a SMS from Kogan saying Welcome to Kogan and an invitation to buy a roaming pack which I didn't.



