alright so you did that canceling and was able to use your upgrade in store or online somewhere else just as fast? (sorry for all the questions im just scared ill cancel and then not be able to get this phone thats available right now and be at back of line)
I did all this about an hour ago. Online availability for in-store pickup locally became open for the 64GB 6+ Space Gray I had on pre-order with Apple. So i decided to take a chance on the timing of canceling the order through AT&T and the Apple Store availability staying active. Turns out it all worked.
If you successfully cancel it in the process I did, your upgrade should be good for use again anywhere you choose.