Second phone line and NBN

I have a first line which is ued for NBN FTTN and a VOIP phone (using non Telstra provider). I also have second copper line.

I just got a call from Telstra for my second line (with Telstra voice only) to be moved to NBN with no charges for the change, and no term contract for the "Local HOme Phone via NBN".

They indicated that Tech will visit premises. What equipment will they install, and will I have any issues if I want to later port that NBN migrated Telstra number to another VOIP provider. 

Thanks/ Sandy