It's not a sure thing, though. There's a slim possibility that Jobs will hold out, especially given the fall-out of the Gizmodo iPhone scoop and the on-going investigation on whether or not a crime was committed. Also, it was previously reported that Apple had book the Yerba Buena Center for the Arts facility on June 22. That date could be for an iPhone-specific event. We simply don't know. Apple, being Apple, hasn't said anything about its plans for Yerba Buena on June 22.
According to Apple, the event will focus heavily on the iPhone and iPad. "This year's WWDC offers developers in-depth sessions and hands-on working labs to learn more about iPhone OS 4, the world's most advanced mobile operating system," said Scott Forstall, Apple's senior vice president of iPhone Software. "WWDC provides a unique opportunity for developers to work side-by-side with Apple engineers and interface designers to make their iPhone and iPad apps even better."
Apple hasn't issued any media invites for the keynote address, nor has it said exactly when the keynote address will take place. It is typically held the first day of the show.