Preview at WWDC likely in June, followed by September launch.
Apple to Hold Media Event on September 7th, 2011?
Apple has traditionally held their Fall media events in the first part of September with the past three events taking place on September 1st, 2010, September 9th, 2009, and September 9th, 2008. Last year's event introduced new iPod touch, iPod nano and iPod shuffle models. This year's event, however, has been widely expected to also incorporate the rumored iPhone 5 announcement. We confirmed with Kodawarisan that the date was not the product of guesswork, but came from a source in the know.
In previous years, Apple has updated the iPhone in the summer during WWDC, leaving the iPod to wait until this September media event. This year, however, without an iPhone upgrade at WWDC, all eyes are on this September event for the launch of the iPhone 5. Apple's suppliers are said to begin shipments of the iPhone 5 in September but AllThingsD has suggested the iPhone 5 won't actually be released until October. It's not clear if that gives Apple room to pre-announce the iPhone 5 in September, or if it means Apple will let September pass by with no mention at all of the next iPhone.
Kodawarisan has been a longtime Apple site that we first referenced back in 2002. We haven't seen many rumors from it in recent years, though notably, in 2009, they did correctly pinpoint the launch date the launch of a new Mac mini.
Update: We originally reported September 8th, but that was in Japanese time. The U.S. date is September 7th, according to Kodawarisan.