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If I remember correctly and history repeats itself, for the 3GS it was about 2 days previous to the online order date that apple announced when they would start taking online orders. If I'm wrong, someone please correct me.

Now the other thing you can do is sign up on apple's website to get notified when the time will be.

Go here: http://www.apple.com/iphone/notify-me/
 
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