Getting a Lumia 920 without a contract

I'm new to the US, and I like keeping my carrier and device separate. I'm using a H2O Wireless prepaid plan, and want the Lumia 920. AT&T seems to have it at $450 without commitment, but still needs a new contract (how they can call that as "no commitment" is beyond me). I don't want a contract - just a new phone. Will I need to get an unlocked version from BestBuy? BestBuy seems to have it for a bit more ($600 for unlocked). I'm in Palo Alto.Thanks!