Pre-orders and previews begin April 10, launches April 24.
Apple Posts Revised iPhone NDA Agreement and Readies iPhone 2.2 Beta 2 Firmware
You agree that any Apple pre-release software (including related documentation and materials) and any information disclosed by Apple to you in connection with Apple Events or Paid Content (defined below) will be considered and referred to as Apple Confidential Information.Apple also restricts "Apple Events" and "Paid Content" which appears to include premium content such as WWDC (which has always been under Non Disclosure). The change is intended to allow the publication of iPhone tutorials, books and collaboration that had previously been restricted by Apple's original agreement.
Meanwhile there have been some mixed reports that Apple has already seeded iPhone 2.2 Firmware Beta 2. If not available now, it appears the update will be available soon for iPhone developers.
iPhone 2.2 Beta 1 had included frameworks for a number of new features including Google Street View and Japanese Emoji icons.
Update: Apple also opened official developer forums at http://devforums.apple.com/.