The butler is fun to have walking around your screen even if its full functionality is unavailable. It will still show missed calls, SMS/email, and it will change appearance during holidays. But when you click on it, you'll see the annoying message that a Docomo SIM is required.
Sharp phones will not normally update outside of Japan. A hack was invented for older models (SH-09D to SH-08E and maybe some newer, but not the SH-01G as far as I know -- check my website for a link to the app and description) that allowed them to update, which is great because the updates fix some issue or other. At some point you might need to send the phone to Japan to get it updated in case an important update or an upgrade to a newer Android version is released. But the phone should work normally even without these updates.
There are some other apps that will not work outside of Japan but nothing you'll miss. You can disable and sometimes uninstall most of them.
Something that you might want to get working but will find difficult to do is voice operation. In older models, only voice commands spoken in Japanese could be registered and executed. But if you manage to learn a few Japanese words and actually get this to work, you'll be sure to impress those around you

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