Can you check if the handset is properly connected to the TPG Modem or NBN connection box?
If you're on NBN FTTN (Fibre to the Node),FTTB (Fibre to the Building),HFC (Hybrid Fibre Coaxial), Fixed Wireless service, the handset should be connected to the TPG supplied modem (Phone 1 or Phone 2) and the VoIP light indicator on the modem should be solid green.
What's the status of the VoIP light indicator?
If the VoIP light it OFF or Flashing Green, try to restart the modem and see how it goes after 2-3 minutes.
But if you're on FTTP (Fibre to the Premises) service, the handset should be connected to the NBN connection box provisioned UNI-V Port (UNI-V1 or UNI-V2).
If there's no dial tone, press and hold the NBN connection box reset button until you see the lights on it flash.
Should the issue persists, send us a private message with your account details so we can check the status of the phone service.