Sony Ericsson K800i from UK Orange

Hi. I have a Sony Ericsson K800i that I haven´t used for many years. I am abroad and the orange mobile phone SIM card shows Inactive when I turn on the phone.
I would like to give the phone to a young nephew down here but when he inserts his SIM card it asks: "Insert correct SIM card"
I took the phone to some local mobile phone technitians around here but non of them know how to unlock an old Orange Sony Ericsson K800i.
Any help on this matter?

You can unlock it in any private unlock shop or search this forum and try to unlock it with patch,but for that you need some expirience and you are doing all at your own risk.

and you'll gonna need the orange SIM card to patch unlock if your phone security got CID53