I found this statement..
Device Protect insurance can only be taken out at the time you obtain a new device from us – no matter if you get it online, in store or over the phone.
Adding Insurance down the track leaves the insurer exposed to people who lose/break their phone then taking out insurance and waiting a month before making a claim.
NB If you have a Optus Lease plan you almost must get insurance.
At this stage if you have a home (or your parent do) you can possibly add specific items to the contents insurance (just make sure they're covered outside the property). This can often be cheaper than actual insuarance plans. I'm with GIO and they also do a general $5000 pool for any damage loss to equipment away from home.