How to find my imei number on a un activated iPhone?

Look I've tried *#06# but because its not activated you can only make emergency calls and i can't find it on the sim tray because its not its original sim tray and i also can't go into setting because its locked and i can't put a sim in it because I'm not in the uk with an o2 sim help
iphone 4 running iOS 7.2

Added (1). Don't have the box brought it second hand

On the box, on the sim tray
and in the phone settings