I called Apple when I first got my 4s and they told me to call AT&T. So I called AT&T and they said I needed to visit a core store in my area. So, I went by there and they attempted to do it, then gave me a number BACK to Apple. So, I called that, and they told me they're suppose to be able to add it for the people that pre-ordered but didn't have the option. The guy was really nice and said to call back tomorrow with the case id. He said their systems were pretty backed up and it's probably related.
So, I guess I'll try tomorrow or Monday