So I've been trying to find more information from a variety of sources on pricing.
The closest to reality that I've been able to find is these leaked details from Optus (via Gizmodo):
"The iPhone will only be available on a 24 month contract – no outright purchase, with the 8GB model to sell at AUD $220, and the 16GB model at $330, with only the 16GB model in white as Steve Jobs announced at the WWDC keynote.
Accessories will only be available through Apple stores – Optus will only carry the iPhone 3G itself, and the all important voice and data plans are as follows: $79 cap for $300 worth of calls and 1GB of data, or a $99 cap with $400 worth of calls and a 3G data download limit.
Visual voicemail is included, and the cap is whittled away in 35c per 30 second chunks, 25c per SMS message and the always annoying but always present flagfall which is set at 30c."
This makes it over twice as expensive as the ATT plans (and I think they had unlimited data). This is where I get cranky about Australian carriers and their stupid plans. It would probably count me out at those prices.
Update: No more Apple rumours. As Brad says in the comments, this is wrong.
Update 2: Looks like the UK is getting a good deal.
Update 3: Gizmodo link gone...nothing to see here.