Essentially, if you want the phone for free you’ll be paying $80 a month for a 16GB version. Every other plan has handset repayments as part of the deal. The bare minimum you can get away with is $48 a month, while the most you will pay is $87 a month, which will get you the 64GB version with 2GB of data and $850 worth of talk and text value
You can check out the full interactive price list over on Optus’s website.