Last month Amazon released the free Kindle application for the iPhone in the US [App Store link], shortly after the Kindle 2 hit the market. If you haven't used it yet, it works quite well. Users can buy books (but not subscriptions) from the Kindle Store via Mobile Safari for reading on their iPhones, although the purchasing process is easier from a desktop browser. Unlike the Kindle, the iPhone app is able to display color images, but it lacks text-to-speech as well as a direct connection to the Kindle Store. Whispersync, which synchronizes ebooks between the iPhone app and Kindle, works as advertised.
A few weeks ago, we posted a comparison of ebook readers featuring, among others, the iPhone app Stanza [App Store link]. As Steve mentioned, Stanza works with nearly every ebook format, even Project Gutenberg etexts. I only used Stanza briefly to check it out and I can say that the UI was very nice. Additionally, the folks who created Stanza have an existing relationship with ebook seller Fictionwise. In fact, Fictionwise created an ebook store just for Stanza users.
This week, we've learned that Amazon has acquired the company behind Stanza. We can only assume that aspects of Stanza will make it into a future release of Kindle for the iPhone.