Oakape - Virgin have been crewing -800s with 4 crew for years! When I was at QF, they'd often do it if someone called in sick. When I was at Alliance (BNE based!) and leased the airwork 737-300 (several years ago), and they went so far as to train us as "NZ based crew" under the NZ aoc - so that they could run the norfolk flights with 3 crew.
Dare I mention the $23,000 base wage for cabin crew?
Aussie airlines will do anything to operate aircraft at NZ costs!