In the License agreement:
Amazon provides wireless connectivity free of charge to you for certain content shopping and acquisition services on your Device. You will be charged a fee for wireless connectivity for your use of other wireless services on your Device, such as Web browsing and downloading of personal files, should you elect to use those services. We will maintain a list of current fees for such services in the Kindle Store
You agree you will use the wireless connectivity provided by Amazon only in connection with Services Amazon provides for the Device. You may not use the wireless connectivity for any other purpose.
Use of Digital Content. Upon your payment of the applicable fees set by Amazon, Amazon grants you the non-exclusive right to keep a permanent copy of the applicable Digital Content and to view, use, and display such Digital Content an unlimited number of times, solely on the Device or as authorized by Amazon as part of the Service and solely for your personal, non-commercial use. Digital Content will be deemed licensed to you by Amazon under this Agreement unless otherwise expressly provided by Amazon.
So it would seem that you'll get charged a fee for any wireless connection outside the buying of books. AND that you cannot read an Amazon purchased ebook on anything (not even your computer) than the one Kindle. (As opposed to the 6 or so devices that can be authorized by MS Lit and Mobipocket).
Via
Jason Griffey