Welcome to the community!
If you wish to have NBN service with TPG it will depend on NBN availability in your area.
If NBN FTTN is available in your area. It is not possible to install a different NBN service while Telstra ADSL2+ is active. Since NBN FTTN will need the copper line to work. Which means your ADSL2+ service with Telstra will needs to be cancelled and upgraded to NBN.
You can visit this link and simply type in your fuill service address to check what type of NBN service is available in your area.
Hope this helps! Cheers!
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