MobileCrunch reports that AT&T has been quietly tweaking the upgrade eligibility dates for the next iPhone. While most of those who purchased the iPhone 3GS at launch had an upgrade date available sometime in November, far be it from AT&T to stand in the way of a new iPhone purchase. They've been changing the dates without fanfare to as soon as June 21st, 2010. That doesn't really confirm anything, but it's almost a forgone conclusion at this point that Apple will release a new iPhone in June. I would say (as a guess/prediction) that we'll first hear about it during WWDC, and that it'll hit store shelves near the end of the month.
Unless there's a big surprise in the pipeline, we've probably already seen this phone as well -- you've probably seen the leaked shots that precluded the whole "left in a bar" situation (that is still under investigation, as far as we know). It's possible that phone was just a prototype, and that Apple won't go for those weird silver buttons, but most likely, that's the phone we'll see Steve holding on stage in just over a month. Excited?