From what I can tell with your explanation of the steps you have taken, you are still running an official ROM that has not required you to unlock your phone. If this is the case, you need to unlock your phone(when you run across posts talking about SPL 2.40, this is referring to unlocking your phone). You have cooked a rom that you would like to put on your phone. That requires you to Unlock first. Here is a link to a thread that has all the info you need:
http://forum.ppcgeeks.com/showthread.php?t=32382
The first link is the one you will want to check out.