Below is a statement provided by Telstra.
3G Network Technology Longevity Statement
Telstra intends that the 3G network will remain in service until at least 2020. Closure activities
may commence from 2020 although initially this is more likely to be simple re-purposing of
part of the 3G spectrum (as 3G capacity becomes freed from migration to 4G) with no
material impacts on our 3G customer base. Full or partial geographic closure may occur any
time after 2020, but would be unlikely before 2022. In any case we will provide a reasonable
notice period of any shutdown activities that would impact end customers. Full closure is
most certainly expected well before 2030. So somewhere between 2020 and 2030 the 3G
network will be shut down but precisely when has not yet been decided.