History of Key Dates

iPhone Release Dates
10/14/2011 Friday 8:00 AM 4s Technical Specifications
06/24/2010 Thursday 7:00 AM 4 Technical Specifications
06/19/2009 Friday 7:00 AM 3Gs Technical Specifications
07/11/2008 Friday 8:00 AM 3G Technical Specifications
06/29/2007 Friday 6:00 PM Original Technical Specifications

iOS Release Dates
10/12/2011 Wednesday 5.0
06/21/2010 Monday 4.0
06/17/2009 Wednesday 3.0
07/11/2008 Friday 2.0
06/29/2007 Friday 1.0

iPhone Pre-Order & Reserve
10/07/2011 Friday 4s
06/15/2010 Tuesday 4

iPhone and iOS Release Announcements
10/04/2011 Tuesday (Let's Talk iPhone event) 4s
06/07/2010 Monday (WWDC) 4
06/08/2009 Monday (WWDC) 3Gs
06/09/2008 Monday (WWDC) 3G
01/09/2007 Tuesday (MacWorld) Original

WWDC Keynotes
06/06/2011 Monday
06/07/2010 Monday
06/08/2009 Monday
06/09/2008 Monday
06/11/2007 Monday

WWDC Scheduling Announcements
03/28/2011
05/24/2010
05/13/2009
05/13/2008
05/01/2007

WWDC 2011 Possibly Scheduled for June 5-9

AppleInsider is speculating that WWDC this year will be held between June 5th through the 9th. They are citing an unspecified "Corporate Meeting" at the Moscone West center scheduled for those dates, which is typically where Apple has held past WWDC events.

This seems reasonable given that for the past 4 years, WWDC has typically been during the first or second week in June. For the last 3 major iPhone releases, Apple has made the official announcement at the keynote of WWDC on the first Monday of the event. Thus, it's possible they will announce the "iPhone 5" on Monday, June 5 at 10:00 AM PST.