Found this on Google, looks like it is valid, I haven't tried it myself. Seems like a good deal to get a discount on Vodafone's Pay Monthly plans, which are rarely discounted. A yearly Warriors Membership can be brought from $30 here, this is required to be eligible. These plans are no contract as well.
The plans with discount:
Advantage Lite - $34.99 (save $5)
* 2.5GB data
* 300 Mins NZ/AU Calling
* Unlimited Texts NZ/AU
Red+ Lite - $49.99 (save $10)
* 10GB data
* Unlimited Mins NZ/AU Calling
* Unlimited Texts NZ/AU
Red+ Essentials - $59.99 (save $20)
* 22GB data
* Unlimited Mins NZ/AU Calling
* Unlimited Texts NZ/AU
I am unsure if these plans are eligible for the $10 On Account Broadband Discount, or if they include the 90 days free Social Pass that the non-discounted plans seem to include. (I'd assume not but you never know!) I will email to find out!
Still a good discount - worth joining the Warriors on a basic membership just for this.
if you are currently on prepay and are thinking about switching to Vodafone, i think Vodafone does a plan like the Advantage light offer for only $$29 a month. It comes with 2gb data unlimited texts and 300 minutes per month. You need to ask in store and you also need to be on prepay. It also includes the on account broadband bonus.