Amazon has pre-announced a Kindle SDK. 

Naturally, this being Amazon, it all sounds way more complicated than it needs to be:

Active content will be available to customers in the Kindle Store later this year. Your active content can be priced three ways:

  • Free – Active content applications that are smaller than 1MB and use less than 100KB/user/month of wireless data may be offered at no charge to customers. Amazon will pay the wireless costs associated with delivery and maintenance.
  • One-time Purchase – Customers will be charged once when purchasing active content. Content must have nominal (less than 100KB/user/month) ongoing wireless usage.
  • Monthly Subscription – Customers will be charged once per month for active content.

Active content applications have an upper size limit of 100MB. Applications larger than 10MB will not be delivered wirelessly but can be downloaded from the Kindle Store to a computer and transferred to the user's Kindle via USB.

Compare this with Apple's pricing structure: apps can be any size you want, priced however you want, with Apple always taking a 30% commission on sales. Of course, neither Apple nor iPhone OS developers have to pay for their customers' wireless usage.

They also pre-announced a new, more-Apple-like royalty split for publishers: where they currently get just 40% of sales, they'll now get 70% minus delivery costs, and only if they agree to certain other criteria (like enabling Kindle Text-to-Speech).

Sony and Barnes & Noble already have competing e-readers out, and Amazon hasn't blinked. Now Apple is merely rumored to be just announcing, not shipping one next Wednesday, and suddenly everything changes.

Next Wednesday is gonna be awesome.