Forgot my iphone passcode, I restored it, but I still need my passcode?

I lost my iphone 4 a couple of months ago and since then have gotten an iphone 3G to replace it, it finally got returned today, but I don't remember the passcode. I tried restoring it on itunes, but it still asks for the passcode. Can anyone help?

Please no "you stole it/found it!" because I didn't, I just need help.

Bye now your probably gonna have to go to a store to get it unlocked. :/