It would end up costing you $199 plus the $175 ETF fee that AT&T would charge you for ending your contract early. There's no way to escape that contract since Apple stores and AT&T are making you activate it in the store and start the contract.
It's certainly possible that the Jailbreak folks will figure out how to unlock it for use with other GSM providers sooner or later (probably sooner). So far, I believe they haven't claimed to crack the iPhone 3G, which uses a different bootloader than the original iPhone.
-------------------- Lisa Gade Editor in Chief, MobileTechReview