It depends on your "Upgrade Eligible" status, if you had a July, August or Sept. date on June 19 then you should see a credit for the $200 based on the method of payment you selected for your purchase.
Just to be clear, AT&T decides if you were eligible for the the best pricing.
If you pre-ordered an iPhone 3G S through Apple's online store, your upgrade eligibility will be reassessed based on AT&T's new upgrade policy for iPhone 3G owners. If you are eligible for the lower price, Apple will issue you a credit for the difference as applicable.
Source:
http://www.att.com/gen/press-room?pid=1574
Did you meet
all of the requirments?
Dave