The units have a HSDPA modem (3G) with a fallback to EDGE/GPRS (GPS). In the USA they use the AT&T network. Outside of the USA a range of providers are used.
With the previous International version of the Kindle, Australian users where charged $2 extra per book, to cover the wireless access cost. It is not clear if this is still the case.
Also Australian users were blocked from using the Kindle's limited web browser (available in the USA). It is not clear if this is still the case with the new model.
The lack of web access must have being driving readers of the Kindle version of my book "Green Technology Strategies" nuts. I peppered the text with hypertext links, on the assumption the average e-book reader would have Internet access.
In addition, the file size of an e-book is not that large, so having 3G access will not make a significant difference to the process of buying a book. The difficulty in getting content into the Kinde from anywhere else than from the Amazon store (compared to other e-book readers) seems a bigger issue. The limited support for multimedia, particularity video, makes 3G less of an issue (a problem common to most e-book readers).
Compared to a paper book, a Kindle is a magical device. But compared to the Apple iPad (or the average $400 netbook), the Kindle reader is a clunky information appliance, with a slow refreshing dull monochrome screen and tiny clicky keys.