This is one of those things that seems to crop up with every iPhone launch, but just to be exceptionally clear; the US price for the iPhone 5 isn't magically "cheaper" than the Australian price. It's also not a very clever idea to import one from the States.
I saw this in quite a few comments on Lifehacker yesterday, as well as all over the Web generally, and via a few in-person conversations. It's pretty easy to see where the confusion crops up from. People watch the keynote -- or just see a screengrab of US pricing -- and then look at the locally announced pricing for the iPhone 5.
If you just took that on face value, then the US pricing is $199 for a 16GB iPhone 5, $299 for a 32GB or $399 for a 64GB model. Makes the $799/$899/$999 that we pay for an iPhone 5 look like the biggest ripoff possible, right?
Then again, at face value, the US iPhone 4 is "free". I'll take twelve!
The difference here is that (so far), Apple hasn't announced outright pricing for the US iPhone 5; those are all two-year contract prices that don't include the pricing for that contract. Apple lists those contract prices on its US web site; so far we don't have Australian contract pricing to exactly compare, but even a very rough translation of current iPhone 4S pricing shows the actual difference.
On AT&T's cheapest Individual Plan, a 64GB iPhone 5 would cost you $299 upfront, plus $59 per month (including data) over 24 months. That's $1715 in total with 300MB of data per month. Looking across the local carriers, Optus' cheapest 64GB iPhone 4S would cost you $1368 over 24 months with 200MB of data. At the time of writing, Vodafone wasn't listing the 64GB iPhone 4S on its web site (and it was out of stock of the 32GB version). Even Telstra's cheapest plan, which comes with 1GB of data -- more than three times as much as AT&T's plan -- comes out currently at $1848. Once you factor tax into the equation, there's either no difference, or it's actually cheaper and/or better value!
It's also worth noting that, just in case anyone was thinking that they could score a $299 US iPhone 5 and then simply not pay the contract, what with being in Australia, you'd be in for a bit of a shock there too -- besides any interesting talks with lawyers, that is.
Despite all the talk of the iPhone 5 being a "world" LTE phone, there are actually three models; an LTE US model for AT&T in the States, a CDMA model for Verizon in the states, and then an LTE model for the rest of the world. We're getting the latter model here, and the US models won't be compatible with current Australian LTE frequencies. Sadly that also means that Australian iPhone 5 users who travel to the States won't see 4G LTE coverage there, although if you do roam onto AT&T it'll present itself as "4G" -- but that's just HSPA+ under some fancy labelling. Just to ward off (some of) the Apple snarking, it's worth pointing out (as this Wired article does) that on the Android side of the fence, there's around nine different models of the Samsung Galaxy S III with the same kinds of network compatibility issues.
That doesn't mean you can't import an iPhone 5 from other parts of the world and save a few bucks; Kogan yesterday announced that it's taking pre-orders for the iPhone 5 and chopping $100 off the Apple Australia price doing so.