As it stands, it is hard to see why someone would buy without a plan because you can opt out of your AT&T plan right after signing up for much less money.  This isn’t a prepaid contract either, AT&T is still working on that… BTW, if you want to see how to get ready for AT&T 3G iPhone goodness check this video if you are a new customer and here if you already roll with AT&T. The AP goes on to say:

  Without a contract, users can cancel service without incurring an early termination fee. But both contract and contract-free phones will be “locked” to work only on AT&T’s network, and the monthly service plans available will be the same, said AT&T spokesman Michael Coe. The plans add a $30 monthly charge for data like e-mail and Web surfing on top of a calling plan. As previously announced, the cheapest monthly calling plan for the iPhone will cost $70 per month, before taxes and fees that can add $10 per month. That plan includes 450 minutes of calls and unlimited e-mail and Web browsing. AT&T is working on providing a prepaid plan, Coe said. A prepaid option was available to buyers of the first iPhone who failed a credit check.