Can I get my Imei number for my 3G iphone? I gave my old phone to a friend, and he is trying to activate the phone, but I need the Imei number! Is there anyone who can help me?

I'm trying to retrieve my Imei number for my old iphone, that I gave to a friend! My wireless carrier said that in could unlock the phone, if I had the Imei number, but I no longer have the phone. I gave it to a friend, and he tried to switch carriers, but can unless it's unlocked, which I can't do on the unlocking website, unless I have the Imei number, PLEASE HELP

-J