Hi @lake62 ,
Welcome to the community!
The Telstra phone line is no longer needed to operate the new NBN service. Once the NBN service installation is completed, you may cancel your service with Telstra. However, if you requested to port your old number from Telstra to your newly installed TPG-NBN, we advise to keep your Telstra service until the porting is completed.
Porting your number to the NBN service usually takes 1-5 working days.
Let us know should you require further assistance.