I know Optus has such deal but Virgin is beating this with $450 value.
I have spoken to the customer service staff on the phone and verified that the $450 value can be used on overseas calls, unlike Optus.
Order online with the coupon code and get 3 months free.
I was about to put in an order but decided to check how Virgin network is. I am with Optus and 3 and must admit I am giving up on 3 when the contract expires.
Virgin is on Optus, same as many others, so shouldn't be any difference to your Optus experience.