The June WWDC keystone address has been the launching pad for iPhone related news in the past. In 2007, Steve Jobs introduced the iPhone. The following year, the iPhone 3G was trotted out to face the public. If a new iPhone is to be introduced in 2009, you would expect an announcement to be made during this year's address. With CEO Jobs not expected back until the end of next month, it will probably be up to Schiller to make an introduction of any new iPhone product.
source: Apple (WWDC), EngadgetMobile (iPhone 3G)