Electricpig is convinced that the iPhone 4S will make an appearance, because they've heard that Apple's UK iPhone PR team is pushing hard for major tech journalists to attend WWDC in San Francisco.
This doesn't specifically point to an iPhone announcement, but certainly we can expect something iPhone related. Originally, it was expected that the normal summer launch for a new iPhone would be pushed back because of the February release of the Verizon iPhone 4. Those suspicions seemed to be confirmed when the first flyers for WWDC touted "the future of iOS and Mac OS X" rather than the future of the iPhone.
The prevailing theory in the tech world is that the iPhone 4S will be a stop-gap device released this fall and feature a dual-core processor as well as a few cosmetic changes (because we wouldn't want any of those iPhone 4 cases to fit the 4S!) It's expected that next year will see the iPhone 5 come with a major redesign.
We aren't fully convinced that we'll see the iPhone 4S just because Apple is pushing journalists to attend. It seems just as likely that Apple wants as much media at the event as possible because, well, they're Apple, and they love to employ the media machine as part of their marketing push.