I love reuniting phones with owners but it sounds like this one is an orphan.
If Optus know the SIM then perhaps you could arrange to send it into some Optus address and ask them to on send it to the owner (if they know it)
Kudos for trying.
Hey @NP66, we'd definitely be able to identify the owner by the SIM card number. What did one of our consultants advise you to do? If we're able to get in contact with the owner, we'd suggest dropping the handset off at your local Optus store. We can then let the customer know that the phone has been located.