1. Turn HTC One X with a SIM card not accepted by the terminal, ie another operator.
2If the SIM card has a PIN, enter it and press OK. If you have set a security code and press OK mark.
3. Then ask HTC One X RED code ("SIM lock code" or "unlock code SIM card").
4 Enter the unlock code and press OK.
Sometimes you need to do Hard Reset [first saves important data (contacts, photos, etc..)].