From the press release:
Customers can already read Kindle books on their Kindle, Kindle 3G, Kindle DX, as well as their iPad, iPod touch, iPhone, PC, Mac, BlackBerry and Android-based devices. Today, Amazon’s wide selection of free “Buy Once, Read Everywhere” Kindle apps is expanding to include Windows Phone 7 devices. Kindle for Windows Phone 7 is the first major eBook application available for Windows Phone 7, and includes new features built into a Kindle app for the first time, including personalized recommendations integrated into the Kindle app home screen and the ability to send book recommendations to a friend without leaving the app. Customers can learn more about Kindle for Windows Phone 7 at www.amazon.com/kindleforwindowsphone and can download the free app from Windows Phone Marketplace.
Great: Amazon couldn’t be bothered to release a Kindle version for the last Windows smartphone OS; but they’ll release one for the Windows 7 OS that just came out (most carriers don’t actually have devices to offer) and hasn’t garnered a market share yet.