How come the new feature I added to my at&t plan not become effective until 2 months from now?

I just ordered a new phone as an upgrade from at&t. I only had to pay $30 for the phone but was required to get at least a $20 messaging feature. So I ordered the phone and added on unlimited messaging for $20 a month. The phone hasn't arrived yet but under my features on at&t's website, it says messaging unlimited (Eff 10/16/2010 ). Do I have to wait 2 months before I can use that?