AT&T spokesman Mark Siegel confirmed for Macworld that activation must be done at the time of purchase, in-store. Siegel also said that customers could keep there current iPhone or AT&T phone numbers and move to the iPhone 3G when it's released.
[ Got the whole scoop on Apple's new iPhone 3G in InfoWorld's special report. ]
According to the speculation around the Internet, you would be able to purchase a subsidized iPhone 3G and not activate it immediately. After 30 days, AT&T would bring up your account and charge your credit card for the subsidized amount of the phone.
In theory that sounds fine, but it does nothing to solve the problem of having hacked iPhones out in the market. That's not to say that this measure will stop hacked phones, but the companies are trying to cut down a peg or two.
The fact that the iPhone will be legally available in so many countries now will also likely cut back on the demand for hacked iPhones.
Macworld is an InfoWorld affiliate.