Amazon recently released a Kindle iPhone app that allows you to read any book that you have purchased. You can use the app without owning a Kindle or in addition to the Kindle. Where the app really shines is using it in addition to the Kindle.
Reading on the iPhone for long periods of time is not optimal compared to reading on the Kindle. The Kindle screen is larger, the battery life is better and the screen is easy on the eyes, with a reflective display.
But what makes the Kindle app great is that your cell phone is always with you, while your Kindle is likely not. Hence, when you are standing in line or on a sitting on a train, you can read a few pages of your current book.
When you get back to the Kindle, it synchronizes your place in the book automatically, advancing the page to where you left off. How cool is that?
The other place I find myself using the Kindle iPhone app is in bed. Since the iPhone is backlit, you can read it without turning a light on in the room, allowing you to read in the dark while your wife is trying to fall asleep. I find the iPhone is also easier to hold when lying in bed, being a bit lighter.
The iPhone holds the same place in my reading life as it does in my photographic life. I own a digital SLR and a point and shoot camera, but the convenience of having a wireless camera in my pocket and full access to my entire collection often trumps the quality of the the dedicated cameras. Like my Kindle, I would never want to give up my DSLR for an iPhone, but they work very well together.
Also, the Kindle works the way iTunes should work. You can download any book you buy from Amazon as many times as you want. The device knows you have purchased the book. Similarly, an iPod and iTunes should know that you have previously purchased a song and give you access. The player becomes a caching device that gets its personality from the cloud, versus being a static copy of content.
On an iPhone or iPod touch, why not just wirelessly sync my purchased music directly from Apple? Why do I need to manage the device by maintaining my iTunes collection on a computer? Yes, I know that Apple does allow buying music on the iPhone and touch today, but this is not a true wireless sync with the Apple mothership. You still need to sync the song by wire to your computer. And if you lose it, Apple will force to buy it again.
Amazon is in the Kindle business so they can sell the media (electronic books) so for them, giving you access on other devices is a no-brainer. Apple has traditionally sold media as a way of selling more hardware, so they probably are not quite a sure they want you to be listening to your music on other non-Apple devices. But I suspect this is changing for Apple. They took the word “Computer” out of their name about a year back and I think they probably believe they are becoming more of a media company.