This is what I was told by an Apple online rep, too. I would have to wait a few days for my upgrade eligibility to be reset, and then I'd have to place a new order. I think that shipping times are a week or two out as well, so I'd be without a phone for a while unless I could get one on the store. I'd love to get the white, but this sounds like a big hassle. Who knows what other glitches might come up in the exchange? Possibly have to fight about my unlimited data plan? I might go to my apple store and see if they'll exchange it, but they probably won't.
I went to the apple store yesterday, and the manager said that I had to return the 4s to apple.com