Preorders for the next-generation iPhone will begin on the same day as its announcement, September 12th, with an official launch on the 21st, say sources for iMore. The people add that a second wave of shipments, reaching international markets, will take place the first week of October, most likely October 5th. Making preorders available on the same day as an announcement would be unusually aggressive for an iPhone launch, since even iPhone 4S preorders opened up two days after an event on October 4th last year.
In the past, however, Apple has sometimes opened up Mac orders on the same day as systems were announced, including the recent MacBook Pro refresh. The company has also gradually improved its launch preparations, ensuring that it's better able to handle supply and order processing issues. A September 21st shipping date would be consistent with claims from AT&T sources.
The September 12th event could be a major one if rumors that Apple will refresh the entire iOS lineup at once and add a "mini" iPad prove true. If so Apple would be doing the refresh to inaugurate its new dock connector format, but iMore comments that it still hasn't heard launch dates for all of the updated hardware. Apple will almost certainly make major changes to the iPod touch and nano, which were effectively unaltered in 2011.