Looks like this deal is back again.
Please check the link for the SIM only plans available.
The Nitty Gritty
3 Months Access Fee Discount: Get 3 months of access fees credited back to your account when you sign up to a new My Plan Plus 12 month SIM Only plan. Available in selected stores. Available via Online, Telesales or Webchat to customers who live in selected postcodes. Visit https://offer.optus.com.au/3mthbyo for participating stores and eligibility requirements. Credit applied from 2nd bill , you will get 1 month access fee discount over 3 consecutive bill cycles. Cannot be used in conjunction with Welcome Credit Port In Promotion.
MY PLAN PLUS SIM ONLY (12 MONTHS):
Cancellation fees apply.
Excludes Business customers.
Discount offer available until withdrawn.