They're hugely different devices, sure, but could the iPhone be stepping on the Kindle's toes again? CourseSmart, which offers subsciption-based, notes-capable eBooks online, has released a full-featured iPhone app for their subscribers. In other words, yes.
The app is free, but you'll need preexisting subscriptions to textbooks in order to access any. It's actually a shrewd, if somewhat obvious move for CourseSmart: lots of college kids have iPhones and iPod Touches, and while taking notes and reading long passages might be a little cumbersome on such a tiny screen, the ability to carry all your books in-pocket, complete with search and bookmarking capabilities, is a pretty big value-add.
As far back as May, it was clear that Amazon was pursuing CourseSmart for e-textbook content, an effort that may have culminated in a wimpy partnership with McGraw-Hill—a CourseSmart partner—which netted the ebook reader, and specifically the textbook-reader DX, about 100 regular old e-textbooks. This looks like something of a snub to me, or maybe just a lack of initiative on Amazon's part, but I get the feeling there's a still a lot going on behind closed doors here.