Using Old Phones with NBN and Netgear DEVG2020

I have a client who likes old things.  He has many old phones which he used to be able ot use on the old copper telephone network. 

Now his premises have been ported over to NBN he cannot connect them and use them anymore.

He is with Telstra and has a Netgear DEVG2020 modem/router on the NBN connection.

He also has a Cisco IP phone which manages his phone service.

I am wondering if there is anyway that his phone service can be managed by the modem and thus he can connect a phone into Phone1 port on the modem and use an older phone?

Or can the phone service be managed by the NBN box and he can plug in older phones direct to the NBN box?

Is this possible with the Telstra set-up or not?