According to a Spectrum Submission to the ACMA by Telstra....

According to a Spectrum Submission to the ACMA by Telstra. Telstra have said that a total of 1000MHz of Spectrum is needed across all carriers to cope with the 50% growth Year on Year of data over the mobile network by 2020. Looks like the ACMA wont be able to free up that much space in time.
The Telco's are looking at all sorts of ways to not buy spectrum... Using Wifi Spectrum for 4G is happening in the US by Christmas... (LTE-U) All carriers are also rolling out VoWifi, in an effort to offload traffic, and improve in-building coverage.