"You can’t buy an iPhone in the United States without a two-year AT&T contract. The first iPhone models had a streamlined feature: You would buy the phone at an AT&T or Apple store, but actually sign up for wireless service at home on your computer. No more.
As with any other cell phone, you won’t be able to buy it without signing a two-year contract. (If you thought the lines at the Apple stores were bad last year, just wait.)
The contract is needed to make the upfront subsidy work. It also will radically cut down on the number of phones that are bought, unlocked, and shipped to other countries."
Above is the quote from ATT Mobility Division's CEO (From New York Times). So it is true, to get 2nd G iPhone, one will need to sign up in stores.