Get an ATA Device

Goldstream have a very good box for just over $60

Simply put an ATA will allow connection of  an analogue (older style) phone to the NBN router and it will give the landline phone experience we are used to. Unlike the phones of old when the power is out you phone won’t work. (VOIP Phones do have their limitations) It takes the analog signal and converts it into something that can be used by the internet. So that favourite little phone you got on special at officeworks is going to be OK.

If your needs are bigger you will be amazed where you can get a phone system adaptor now. Even places like Kogan sell things like this amazing phone system. And for only about $800. The Technology is really bringing down prices and giving small business the tools it needs to compete with the big boys. That also means your investment in things like messages on hold are not wasted.

All you need is someone to explain it to you. Or have a good google.

More info here here and here