The Labor government setup a new company NBNCo to manage the rollout of the new (mostly) fibre network.
However it really made no commercial sense to have two cables going each premises and pay the costs of maintaining them both, so the decision was made to turn off the copper cables in favour of the new fibre as it was rolled out. An agreement (called the definitive agreement) was struck with Telstra (the private company who owns the copper cables) to allow NBNCo to use their pits and ducts and to turn off the copper network in return for around $11 billion of compensation.
The problem now is that all the telephone calls that used to go over the copper now have to go over the data fibre. In a sense currently we send the internet over the top of a telephone network (ADSL), whereas we will be carrying telephone calls over the top of an internet network.
Typically 18 months after fibre is switched on in an area, the copper network is switched off. Everyone (including businesses) who uses the copper network for regular phone calls or ADSL based internet must transition during this time. There are some services (mainly ISDN) that are not being switched off. It is important to note that this is driven by the agreement with Telstra. There doesn’t appear to be much opportunity to delay this switchoff date.