Chat with Optus and they said if you sign up to any mobile service as a second service, then you get a $10 off per month.
This cannot be combined with student discount.
Some pretty good deal to own the phone:
1. iPhone XS: from $65 per month.
2. iPhone XS Max: $85 per month
3. Pixel 3 XL: from $75 per month.
4. Huawei Mate 20 Pro: from $74 per month.
5. Note 9: $85 per month.