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I live in South Africa, and I don't see the iPad arriving here till much later in the year, so I asked a friend of mine who is in the states on business to get 2 3G iPads for me (from what I've read it's pretty simple to cut the regular sims down to micro sim size). He's tried all the stores in Las Vegas and Chicago. No luck whatsoever. The one salesperson at one of the stores told him they receive about 100 per day and they sell out in a few hours.
 
If you are anywhere near a university that has a computer shop, check there. Mine sells Apple products, and has a dozen iPads on hand. The students have left for the summer, so sales have slowed to a crawl.

Yep, my local U also has several in stock in their campus Computer Store. Unfortunately they don't carry any of the 3G models, or haven't had them in stock yet anyway.

Nine non-3G models in stock right now... (have to scroll down)

http://cstore.msu.edu/pricelists/instockspecials.asp
 
I got an email today from my local Apple store letting me know they got the 3G ipads back in stock. This is the Easton store in Columbus Ohio.
 
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