Since I have received an email from TPG that my TPG NBN Bundle service was active, I have contacted Telstra to terminate my land phone number.
However Telstra said they needed to be requested by TPG to release the number when porting from Telstra to another provider. I thought TGP had requested Telstra to release my land phone number already, I am confusing.
I certainly can see given Digital Voice Number by TPG is my land phone number. Do I really need something to Telstra??
TPG does request Telstra to do the porting, whatever that involves.
If you have confirmed that your landline phone is working via the NBN connection, you only have to cancel your phone service with Telstra, otherwise they continue charging you. (Seems like porting a number to another provider doesn't trigger any action with Telstra billing. This has been reported by other users.)
The procedure is, if you want to port your original phone number to TPG, you had to wait until the porting was completed, before cancelling the service. If you do it the other way around, your number might be allocated to someone else.