I have never been North of the Whitsundays but phone/internet is bad enough there plus its very patchy North of Hervey Bay and in the islands.
We use a Satsleave sat phone
thing that converts your iphone
into a sat phone
and that proved to be a good thing for phone and texts, not so good in my experience for internet
I would think a sat phone is well worth the $15 per month to have on board.