You can buy all sorts of Chinese phones (with dual SIM) directly from China online on sites like Aliexpress.com. The thing is, US uses weird 3G frequencies or something from the rest of the world.

I bought my 3G MTK phone a year ago on Aliexpress.com. It worked fine perfectly while I was living in Europe. Then I came over and now I'm always on Edge network and network speed is significantly slower.