Once you have received the "unlocked" message, please follow the following instructions carefully.
- Install last version of iTunes
- Make sure phone is updated to the latest official version from iTunes
- Connect phone to iTunes with not accepted (not valid) SIM card
- Wait until iTunes detects phone
- Now disconnect phone and reconnect after 10 seconds
- Phone is Unlocked
- Insert a non accepted SIM card
- Connect phone to iTunes
- Perform a back-up (if necessary) then restore
- iTunes will display "Your Phone is Unlocked"