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The Apple Time Capsule appears to be a router only.
For your NBN HFC to work, you need to connect an NBN compatible VDSL Modem-Router to the NBN Arris Box.
We'd like to set your expectation that if you are to use your own NBN VDSL Modem-Router, the VoIP service will not work as it is only configured on the TPG supplied modem.
Let us know should you have further queries. Thank you.