I am in the US for several weeks.My iPhone is not working. I have it subscribed to service in Okinawa Japan.
  
  Should my iPhone be working properly to make calls and send MMS, and check email?
  
  Is there something I need to do to make it work? Thank you.
  Added (1). Thank you Tech One. But do I have to change carriers while I am here? I am still active with my current carrier from Japan.
  >>> Will my iPhone work in US while here from Okinawa, Japan?