The iPhone, fast becoming the most widely used smartphone globally, while not as reader friendly as the Kindle, and the iPod Touch, are both mass market devices which are selling by the millions each month.
In addition, the iPhone and the Touch are excellent mobile Internet devices with relatively large and readable displays which can easily handle the Kindle e-reader application. Unlike the Kindle they are also pocket-sized devices.
According to a number of reports, the Kindle application for iPhone will include Whisper Sync that enables a user to bookmark a page on one device and pick up reading from the same page on another device with the Kindle application. That would presumably mean that users could read an e-book across a variety of Kindle compatible devices.
The Kindle will be downloaded from the Apple App Store. Some have postulated that Amazon is hoping to spark increased interest in the Kindle by making its application on the iPhone. However, the move could just as easily be viewed as the beginning of spreading the Kindle application to other platforms such as netbooks and tablet computers.
After all, while Amazon is in the business of selling anything it can online, content in the form of books and now e-books is still its primary business. If Amazon can make Kindle a defacto e-reader standard on a billion devices worldwide the company will have gained the sort of dominance it could never achieve trying to selling a nice but expensive niche product.
Look for more announcements about the Kindle application being available on other hardware platforms soon.