Apple Insider believes Apple may introduce the next-gen iPhone at WWDC 2010:
A calendar listing for San Francisco's Moscone Center has led to speculation that Apple's annual Worldwide Developer's Conference will coincide with the three-year anniversary of the original iPhone's launch.
The Moscone Center Calendar lists a "Corporate Event" from June 28, 2010 through July 2, 2010 in the Moscone West hall. Previous Apple events have been reserved with the same title.
This year, WWDC 2009 ran June 8 through June 12. In previous years, the event has marked the introduction of new iPhone models. This June, Apple introduced the iPhone 3GS.