He gave me this kind-of riddle?

So I'm talking to a guy who just bailed on me for something important, but he asked if I had an ipod/iphone which I do then said that his code was "---" (<-4 digit code there) and for me to "work it out" then went off to do the thing he bailed on me for. I've tried googling it but I'm at a loss, anyone help me out?

He shouldnt do that just talk about it

Well you have to tell us the code in order for us to try and work it out or how do you expect us to help you?