Not sure if you've chewed up all your data allowance on your Optus iPhone? While you've always been able to check your account details online, Optus is now offering a free iPhone application to keep track of that information.
One you've signed up for Optus online 'My Account' service (for either prepaid or postpaid models), you can track your usage patterns and available credit using the free app. Optus' launch will presumably spell death for the several paid applications which serve the same function — for one thing, they can't offer unmetered access for downloading and using the application, or include top-up and bill payment options. Optus does warn that the data can be out of date by up to 24 hours.
Optus My Account [iTunes Store]