Hi @JeffreyL . TPG NBN plans include VOIP phone facility. When you took up the NBN plan, you had the option to port your existing home number or be given a new number. The VOIP function is pre-configured into the TPG supplied router, which must be the device connected to the phone socket. A BYO router cannot use the TPG VOIP function. There is no user configuration available.
You don't need to use it or even have a phone connected. There is a 0$ PAYG plan with no included calls which needs a pre-payment to make calls, or some pay-for plans with included calls.