Jetstar doesn't fly any pacific island routes from AKL, they only fly domestic & trans Tasman.
Pretty much Air New Zealand & Virgin are the only two airlines that offer budget flights to the pacific islands.
There also is Air Pacific (Fiji), Air Calin (Noumea), Air Vanuatu (Vanuatu), Air Tahiti Nui (Tahiti). All of these carriers only fly to AKL a couple of times a week & tend to be full service airlines pricing wise.
By far Air New Zealand, has the best route network/frequency.
They fly AKL-NAN/RAR/PPT/VLI/NOU/APW/TPU
Routes like NAN/RAR on Somdays of the week get double daily services