Harvey Norman is offering 10% off plan fees at Optus if you port in with them (no discount on handset portion). Stacks with Optus' promotions, e.g. $106.25 plan for iPhone XS & Pixel 3XL.
If you are a student, you can get an additional 10% off the original plan fee as well if you ask them to apply it in Live Chat after signing up e.g. $106.25 plan with 20% (10% HN & 10% Student Discount) off ends up being $85pm. I signed up for a 3XL last week on the $106.25 plan, and successfully have both discounts applied.
Was denied student discount in chat