The Kindle Reader app is now available for the iPhone. I tried it out this evening, and here are my initial impressions.

Device registration was painless: sign in with Amazon username and password associated my iPhone with my Amazon account.

There appears to be no way to purchase content from inside the app – users are directed to either go to their computer or use Safari on the iPhone. Although this is less convenient, I could also argue that it would be too dangerous for me to want to keep this app around otherwise – between the ability to purchase content from inside the app and one-click buying, I’d be worried about exceeding the limit on my credit card!

I went to the Amazon web site and browsed around for titles I might want to read, all the while thinking about where I would be able to use the iPhone to read these books. I don’t have a Kindle, so this would be the primary (really, the only) point of content consumption. I also solicited reading suggestions on Twitter, and @solcita suggested I check out Palimpsest by Catherynne Valente. I was pleasantly surprised by the ease with which I was able to request a sample.

Unlike the Kindle devices, which I understand run Whispernet content synchronization in the background, I believe the Kindle app has to be active in order to sync the content with the Amazon digital store. The sample came down over AT&T’s 3G network in about a minute.

I started reading the sample and came to the conclusion that this was not a book I would want to be reading on such a small screen. I now have this idea that some books are better-suited to reading on an iPhone than others.

Books that are “snackable” (i.e., consumable in small pieces at a time) are probably better suited for consumption this way than ones with long chapters. You know the kind — when you reach the end of the chapter, you’ve all but forgotten how it began. So much for my grand idea to read Neal Stephenson’s Baroque Cycle on my iPhone while waiting in line at the supermarket or the DMV.

The display on an iPhone is nice, but not as easy on the eyes as the eInk display on the Kindle. Yet another limiting factor for how much content one can consume in a sitting.

I ultimately decided to go with William Gibson’s Pattern Recognition. The download hit a snag, but I was able to hit a retry button and eventually got the content downloaded. The whole thing took about 8 minutes to download. As I said, I believe the app has to be active for the download to take place. This may be an issue for some users (like me), who would prefer to check email, tweet or make a phone call while Whispernet is doing its thing.

Overall, I would say it’s an interesting app with lots of potential. I’m willing to take it for a spin, but I think I still prefer paper overall. I’m curious to see how they extend/improve this app going forward, though.