Soon, publishing for distribution in the Kindle Store will no longer be available through Mobipocket.com. Publishing and selling in the Mobipocket.com store and other Mobipocket partner retailers will not be affected, but the Digital Text Platform (DTP) will become the preferred path to publishing on Kindle. In the coming weeks, we would like to begin consolidating your titles into one location – DTP.
We’re writing to remind you about our earlier message, and to again offer assistance with moving your Mobipocket.com titles to DTP. By making the move, you’ll be able to take advantage of the new royalty options and great features available only on DTP.
You may already have a DTP account, but if not, please sign up today at http://dtp.amazon.com/
When I first read this, I could have sworn that Amazon already did this months ago. It's been so long that I honestly couldn't remember when it happened. But with a little digging, I found this notice on the Mobipocket EbookBase website from last year:
Effective September 2009, we will no longer open new accounts for publishers to sell titles through the Kindle Store or MobiPocket.com. If you have an existing account, there will be no change and you can continue to upload and sell titles using Ebookbase. New publishers with a US address and bank account can sign up to sell ebooks in the Kindle store via our self-service publishing channel at http://dtp.amazon.com