Back in 2018 I did a trip through the desert regions in the northern part of South Australia.
(Lyndhurst up the Odnadatta track and then later back down to Mt Dare etc)
In that part of Australia (2018) Optus was the only service provider with any decent coverage.
Many tourists bought an Optus package when they discovered this on location. The kicker was, even Optus signal was so weak you couldn't log on and complete the set up without dropping out.
So you needed to set it all up before you left civilisation, but sketchy calls/texts were better than zero Telstra coverage. (unless you were trying to escape)