Michael Mace does a detailed analysis:
The immediate impact of the iPhone is that it changes the terms of the debate for everybody. Every new mobile data device will be evaluated against the iPhone’s specs, which is going to become very irritating for a lot of vendors because the iPhone isn’t shipping yet. It’s like boxing a ghost. I suspect that may have been Apple’s intention. Supposedly it had to announce now because the device would have leaked when it entered FCC testing, but an interesting side benefit will be that Apple can stall sales of all its competition. I think this is likely to be a very unpleasant time for Microsoft Zune, a moderately unpleasant time for Palm, and an intense annoyance for everyone else.