Looks like I'm a bit late to this thread, but there is a HUGE world of difference between the Kindle 3G US model (B006) and International model (B00A) in terms of free 3G coverage. This article covers it well:
http://the-gadgeteer.com/2012/02/03/...-of-the-world/
If you don't believe me, then compare the coverage map for yourself...
US 3G coverage:
http://client0.cellmaps.com/viewer.html?cov=1
International 3G coverage:
http://client0.cellmaps.com/viewer.html?cov=2&view=intl
For example, I live in Singapore and travel to Vietnam every month, and I would've been better off with the International model because the US model offers only EDGE support in Singapore and _no_ coverage at all in Vietnam. If you live in Australia then you would be better off getting the US model because AT&T provides superior coverage to Vodafone in Australia.