Update, 20/12/2024: I shouldn't leave my audience hanging. A few weeks after writing this, I had a working phone, but there was a snag with transferring my old number over. As this was now at the pointy end of the academic year, I hadn't the time or spoons to deal with this, but I could at least make and receive phone calls. A few weeks later, my assignments all submitted, I finally got that sorted. Numerically, I'm me again!
Granted, I knew this was coming. I'd heard from better informed people than myself that although my phone works on Vodafone's network, which had switched off it's 3G support in January, it would not work on Telstra's network when it came to decommission it's 3G.