This happened internationally earlier in the day, but now Apple has sold out of its U.S. iPhone 4S pre-order allotment. Customers who are interested in ordering an iPhone 4S from the Apple Online Store can still order, but the shipments are said to arrive in 1-2 weeks. The one week likely means just a little after the October 14th launch, and the two weeks would be right around October 21st.

Thanks Akotin23!