I won't work unless its unlocked using a turbosim, however not sure if they will work with the new iphones (turbo sim is a small chip that slots in along with your own sim)
Other option is jailbreaking it - loaded non apple OS that doesn't have the restriction on networks. Typically it takes a couple of days/weeks for a new release to get broken but would off getting a new iphone 3g S until you know it has been done successfully.
Final option is to buy it in a country that doesn't allow phones to be sold with a sim lock - Italy, Begium, maybe France, could be a few more.