Limited 2 per customer.
I am not sure how many months it can last. Will previous method such as change the plan to $21 pm or what so ever can still be used?
Free 2hr delivery to within 10km of store as well.
By the way, this can also be used to "charge you existing account" (which i believe is a grey area and only available once per 6 months) by "activating replacement sim" option.
To make it last 3 months you need to pay an extra $7 now. So $45 + $20 referral equals $65 credit.
Still $27 for 3 months isn't bad if you want a break from Sim slutting monthly but not much data (39GB). The good thing is data slows to 1Mbps if you use it all.