It's not really much of a surprise, but enterprising Whirlpool forum posters have discovered that Optus recently updated their pricing document and when it comes to your iPhone data allowance to specify that the included data cannot be used for data tethering. In other words, in order to use your iPhone as a 3G modem, you're going to need to pony up some extra cash, at least if you're on Optus. There's no official word on what that pricing might be, but a post on the MacTalk forums (that has been removed) said that we'd be looking at $15 for 500MB. That's still well and truly in rumour country, but if it is accurate, then the whole appeal of tethering your Optus iPhone just lost a whole heap of appeal – why spend $15 a month for 500MB when you can get double that for $20 a month on 3, including a 3G modem?
*UPDATE*: Aside from fixing my glorious 500GB typo, the guys at MacTalk just pinged me to say that their post was posted in error, which is why it was taken down. The Whirlpool discussion is still very much accurate though, which is the main point here anyway... [Optus Pricing table (doc download) via Whirlpool Forums]