Telstra just brought out a new deal that discounts $240 off any postpaid smartphone/tablet when you purchase an eligible Telstra plan. Works for existing customers upgrading and new customers.
Works in conjunction to the previous $50 byo/12 months with 7Gb data and $200 credit (bringing it down to $33.3 if you stay over 12 months) (https://www.ozbargain.com.au/node/217715)
This brings these devices to the following prices:
Nexus 5X 32GB $480
Sony Z5 Compact $525
Sony Z5 - $768
Samsung Galaxy S5 - $360
LG G4 - $504
Huawei P8 Lite - $96 (includes a Huawei Smart Band)
Other phones are available too
Applies for tablets!
Eligible plans include Telstra's Go mobile plans, go mobile BYO and go business.
If you stay on the plan for 24 months, you can also get a data shared sim (extra 1GB) and an iPad mini 2 16Gb for an extra $18/month
Available both online and instore
Yep instore is the way to go.
I recommend ringing a store or two to check they have stock.