A June release is a mistake, IMO. That's just too close to the next iPhone release, and I would be forced to wait to see what Apple had up it's sleeves. I'm pretty sure I won't be the only one with this mindset.
I wouldn't count on Jobs to ever admit that a larger phone with a 4.3 inch screen would be the way to go so I expect the next iPhone to be virtually identical to the current one as far as size (physical and screen) are concerned. Here's what I expect the next iPhone to improve on: faster uP, more memory (RAM and flash) -- that's about it. Remember, Jobs is infallible and the phone he designed will never need to be changed because it was and is PERFECT!
My iPhone 3G contract is up in July so I should know for sure what the next iPhone is going to be like before I decide which way to go. But, at this point I'm leaning towards one of the new HTC phones with 4.3 inch screen.
Brian