iPhone 4S cannot send messages
Go to Settings &gt; General &gt; Phone (or Settings > Phone, depending on iOS version), and see what it says underMy number`. Chances are it still has your old number, if it does, change it to your new one.

Does your old Japanese number have a check mark next to it or is it just greyed out in Messages and FaceTime?

What does it say when you try and send a SMS? What error message are you getting?

Is this only for iMessage or ALL SMS?

Is your Data working?