As is not unheard of for the company, Apple is already beginning to stockpile units in the United States for quick distribution to carrier partners, other third-party retail partners, and its own channels. With the new iPhone hardware expected to be introduced at next Tuesday's media event, Apple's past history would suggest that the new models would launch in the U.S. and other first wave countries about a week and a half later, with Friday, September 20 being the most likely date.
The site also notes that C Technology has claimed on Sina Weibo that 1.2 million iPhone 5Cs were shipped the to the U.S. yesterday. Recently some photos were leaked online that claimed to show their retail packaging.
MacRumors is unclear if the iPhone 5S is in the shipments they've been hearing about.