When a product is hyped and there is a huge amount of interest, a common problem on launch is supply shortages. We've seen it with video cards, with processors, with game consoles and many others. Will it happen with the iPhone? Supposedly not, as according to some reports there will be over 3 million iPhones ready come launch.
Of course, Apple will not comment on these reports or other launch speculation. That said, they have claimed they want 10 million sold before the end of next year. Given the only slightly-more-than-niche market that PDAs are, and given the high cost of the iPhone, that's gonna be tough. Still, if supply is always there, they'll have at least one leg up.
As the article brings out, they face some serious competition. Nokia, Palm, Rim, HTC and others are already well embedded into the PDA market. Even if three million out the door at the end of his month could happen, it isn't what Apple is used to: The iPod often faced artificial shortages intentionally. Perhaps they've changed that business model. We'll see.