theres no differernce they are same you can buy it from europe and use it on t-mobile 3G or buy it from US and use on european 3G networks,
theres no special n900 for US at this time which is reason why theres no 3G support for most the north american networks and its only for t-mobile usa 3G from what i understand, of couse you can still use it on any other network if u dont care about 3G and are happy with edge