Here is a pdf you may find worthwhile reading if you are getting FTTP (and it does allow for multiple telephone sockets in the house):
In particular from the FAQ section, It advises you can have 2 (two) separate phone services and that you can have multiple phone and data sockets cabled into your home that connect to the NTD:
Can I connect other devices to the unused ports on the nbn™ connection box?
Unlike modem/routers you might be familiar with from ADSL and cable broadband services, each port on the nbn™ connection box is reserved for a separate service. This allows you to have up to four separate broadband data and up to two separate phone services through one connection box. If you only order one broadband service, then only one port will be active. If you connect one of your devices to an unused nbn™connection box port, your devices won’t be connected to a phone or internet service.
I have a monitored home or premises security system.Will it work over the nbn™ network?
It is expected that most monitored security systems will operate over the nbn™network. However, if you would like to use an existing system, you should check with your security provider to ensure that your particular equipment and service is nbn™network compatible. You should test your alarm the same day that your service over the nbn™ network is activated by your service provider, and also check that your in-premises wiring is correctly connected up to your service over the nbn™ network. For further information on alarms and the nbn™ network, visit nbn.com.au/alarms
Can I install in-home cabling myself?
nbn will professionally install the cabling from the street to your nbn™ connection box (for more information on what’s included in a standard installation please visit nbn.com.au/fibreinstallation). If you choose to install additional permanent phone or data cabling through wall, floor or ceiling cavities it must be done by a cabler registered with an Australian Communications and Media Authority (ACMA) accredited industry registrar. Your service provider may also be able to recommend a registered cabler in your area. Other non-permanent cabling such as plugging your own router or phone into the nbn™ connection box can be done yourself.