Amazon’s Kindle ebook reader just gained the ability to purchase and download Audible audio books directly over WiFi. Previously, Audible audio books could only be transferred using a USB cable connecting the Kindle to a computer.
The Latest Kindle Offers Wireless Delivery of Audible Audiobooks via Wi-Fi (Kindle Daily Post)
Audible content is available for purchase as a section under the Kindle Store. It is not clear how this ties to an existing Audible subscription account. I did not, for example, see a way to retieve Audible audio books I have already bought over WiFi.
You might have noticed that Amazon specifically notes that Audible audio books are delivered over WiFi. This is because audio book files can sometimes be quite large (hundreds of megabytes). The 3G Kindle is bundled with free lifetime 3G wireless data service. Its cost is presumably covered by some initial fee plus some fee that Amazon pays AT&T (or Sprint for older devices) for ebook data file transmission. This negotiated fee was for relatively small ebook files, however. Moreover, huge audio book files would take a very long time to download over typical 3G speeds.