If you entered everything in correctly, you now have a working US phone, with a real phone number that can be used anywhere in the world with a net(WiFi) connection.
Such is the case with a trio of WiBro-capable PDAs being marketed under the Flyvo brand by POSDATA, all of which run Windows CE 5.0 Professional Plus on an ARM processor and let you get your 'net on with WiFi as well in case you have to travel outside of Korea.