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I think you have to "hack" it a little, but im not sure. I know its possible, but not sure how you get around doing it that way. Why dont you just get the iPod Touch?
 
You need to

1) Fail the credit check (enter a series of 0s in the social security number)

2) Take out an AT&T pay monthly plan (which you can subsequently cancel)

You need this to be able to activate your iPhone.

3) Activate the phone.

4) Cancel the contract

5) Enjoy your 'Super iPod Touch' which will do things that the iPod Touch does not - eg e-mail via WiFi, etc.
 
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