Hi Max,
I take it you have read these two threads:
You can’t expect more than comment and advice in this forum.
A reliable service can only be guaranteed through a collaboration between the manufacturer and the operator, so it’s not about a country but about an operator. Operators may not provide coverage throughout the country.
I advise you to ask the Australian operators directly. You will be able to judge the quality of their services from the quality of their replies.
I also advise you to ask Fairphone, though they may well reply that they do not guarantee support of their devices in your country and cannot reply to your question.