These SIM cards are usually pretty cheap anyway ($1 each) but you can get them 20% Off using the code: SASDEC21 from this post - https://www.cheapies.nz/node/31049
Free shipping codes can't be used for these on their own but will work if combined with something else on your order.
Note: The SIM comes with $5 of Warehouse Mobile credit (not a $16 combo like their picture shows!)
These SIMS are great even if you are not a Warehouse Mobile customer.
I use them for things like the Waitomo Spin to Win promotions where for for the cost of an $0.80c SIM you are guaranteed at least $2 back.
What's more you don't have to activate the SIM straight away. For Waitomo spins you just need to enter the mobile number to collect the free fuel.
This can be done over a number of different Waitomo promos and you only need to activate the SIM at the point where you want to redeem the value on it, as long as you use it inside 12 months as this is how long the Waitomo Moolah lasts for.
Update: You can get it even cheaper - for 0.72c from Warehouse Stationery
Use the code SASDEC21 but also stack with the WELCOME10 code for another 10% off
Proof here: Warehouse Mobile SIM for $0.72c