a VOIP service at $4/month including DID and free landline calls within Australia (that I do on the mobile anyway)
Australian Phone Company - Residential VoIP - Home Phone Service Plans
Their VOIP service and price is right, and I have had positive interactions with the support staff. I found them when I was testing VOIP services looking for one that worked with regular POTS fax machines. I also discovered that entry-level GrandStream ATAs do regular POTS fax better than the Cisco/Linksys/Sipura entry-level ATAs. I'd given up years ago trying to do fax over VOIP, but then I discovered that faxing on Optus NBN VOIP to TPG NBN VOIP worked great, so I gave it another shot.
On a related note: my parents had copper home phone and a faxstream duet piggyback number for their fax machine, with distinctive ring so that the fax machine only answered fax calls (although that didn't stop my parents trying to answer them too). This has worked great for years, but... then they were forced to change to NBN. I'll spare you the unhappy details, and tell you what I should have done.
The NBN changeover process does not cope well if you have a "complex service", ie anything other than a single phone number on a single phone line. If you have extra phone numbers on a line, you will probably lose those extra numbers when porting the service to NBN. What I should have done is port the extra numbers away from the POTS provider and to a VOIP provider, so that all that was left on the line to be changed to NBN was just a single, simple (not complex) telephone number and service.
Live and learn.
Things are actually better now than they were. My parents never really grasped the concept of two phone numbers on one line. Now that the phone and fax numbers are on different separate independent services, and they can send/receive faxes whilst talking on the phone at the same time, my life is much simpler. ?
One last little tip is that TPG has a basic NBN phone line replacement plan $30/month with PAYG phone calls, or an extra $10/month for unlimited non-international calls. It comes with a router and 10 GB/month of data too, so if you're careful to keep within that data limit, it's great for doing email, news and online sudoku. We did get stung a couple of times by devices doing iOS updates at 3 GB a pop but, once we sorted that out, it's been smooth sailing since.