John Gruber of Daring Fireball, certainly no stranger on this site to iPhone news, rumors and speculation, is positive tomorrow's event will feature an "iPhone 3GS".
What does S stand for? Don't ask. He doesn't have a clue. What he does think he has a clue about is pretty much everything else that will pop out of Apple execs' mouths at WWDC this week.
The iPhone 3GS:
I expect Apple to announce updated iPhones with significantly faster processors, twice the RAM, and twice the storage. I expected prices to remain the same as the current lineup: $199/299 for 16/32 GB, respectively. The video camera is going to be a major selling point.
I believe this is true, and the new price will be $99. But since I expect the new top-of-the-line iPhone 3GS to start at $199, that means the $99 iPhone must be something else. I see two possibilities: (a) a new device, something that is to the iPhone what the iPod Mini was to the original iPod; or (b) the existing 8 GB iPhone 3G, unchanged but reduced in price.
And an iPhone nano might round out the three tiered line some day, but not tomorrow.
While I am convinced that "Marble" is a real design project at Apple, I no longer believe it is slated for Snow Leopard. A new visual appearance isn't something Apple can spring on third-party developers at the last moment. If they plan to ship Snow Leopard soon - say, by the end of August - that just isn't enough time to allow developers to update their software to look good under a new UI theme.
Oh, and that about tablet thing... Gruber seems to think it exists in some shape or form, but don't expect it tomorrow. Like the rest of these predictions, that sounds pretty safe. [Daring Fireball]