The bit that "worries" me is that on the JB Hi-Fi webpage it does mention that
"The S1700 off the purchase price of a Samsung Galaxy Ultra phone (referred to as the "JB Hi-Fi Voucher" in the Telstra Terms and Conditions and replacing the dollar value of the Voucher in the Critical Information Summary) "
I know I may be reading a bit too much into it.
It does not matter. You are opting for a service and following the rules. If they have an issue, they can update their T&C.