The fact of the matter is that the device CAN do 4G -- what people in Australia do or can't do is up to those carriers. The device is a 4G device and people living in certain areas need to be aware of the limitations in their country or area.
I lived in area that for several years only had EDGE. I could not use a 3G iPhone so I never upgraded. I never even considered suing Apple or AT&T because I didn't have 3G. I knew the limitations of AT&T, my provider.
Bottomline, when Apple sales a device, it knows not where that iPad will end up. It could end up on the other side of the world. Apple is an international company and the iPad is an international device.
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I would certainly imagine that customers were advised over the limitation when the bought theirs. There's a lot of dialogue between customer and salesman with advice and instruction happening during the purchasing. I know when I went in to buy two iPads the day after iPads when on sale, the salesman was nothing but helpful, answering all of my questions and offering suggestions and advice. I was with him for about 15 minutes even though it was a straight forward purchase.
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The funny thing is that, even with customers being able to return the things, I would bet that most will not do it. They love the new iPad and most knew what Telstra could and couldn't do -- why? Because most already have cell phones and know firsthand of the limits. But even with Apple emailing and offering refunds, the government will stay in a tizzy and eventually fine Apple big money over this. Apple can't win.
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Here is what Apple small print says right now on the Aussie Apple website:
2. 4G LTE is supported only on AT&T and Verizon networks in the US; and on Bell, Rogers and Telus networks in Canada. Data plans sold separately. See your carrier for details.
Here's a page specifically about Internet service:
http://www.apple.com/au/ipad/4g/