You need to ask o2 to unlock it so he can use his sim @Ooooooooo.
Put your sim in the phone for a couple of days, then request the unlock in your "my o2" app.
Some more advice on unlocking in the guide below@
Guide: Unlocking an O2 phone to use a different SIM card
Please note, this is not customer services and we cannot access your account. Do not publish personal details (email, phone number, bank account).
Link to our guide on how to contact them can be found here
