One hitch I noticed when I tried ordering 5c last week--just to see how the preorders for 5s might go...
Do not select the use this phone internationally. For some reason (maybe it's my unlimited plan feature or blocks or something), I couldn't complete my 5c order and had to click back numerous times. I gave up and started a new order, which was a total waste of time.
Alas, I quickly got my 5s order in with a new SIM.
Good luck, everyone!