In early February we reported that Amazon was working on bringing the entire Kindle book library to the iPhone. Well folks, that day has finally arrived.

Late last night, the Kindle for iPhone application was placed at the App Store. The application is free to download, and it allows users to read already purchased books from the Kindle Store. The Kindle Store has over 240,000 books available. Most new releases and bestsellers are priced at $9.99, and customers are able to preview the first chapter for free before purchasing.

The application is able to sync your place in a book with Amazon’s servers. This means you can start reading a book on your iPhone and switch to the Kindle without ever losing track of where you are. Kindle for iPhone supports bookmarks and text size adjustments as well as the ability to view annotations created on the Kindle. The application, however, doesn’t allow users to create annotations on their iPhone.

There are a few catches involved. The iPhone application doesn’t allow users to actually purchase books through the application itself. Users are required to purchase the material through the Kindle Store using a computer or the iPhone’s web browser. Once purchased through the store, your iPhone will sync with your online library.

The application also doesn’t support newspaper or magazine subscriptions. Only books are supported.

If you already are a Kindle user, this is great news. You will now be able to read your entire library on the go, even when you forgot to take your expensive book reader with you.

It will be interesting to see how many non-Kindle users actually use the service solely on their iPhone. Will you be one?