"Unlimited" 3G wasn't mentioned, people are just adding that in themselves!
From the wayback machine
showing the Kindle 3G pre-order page on Amazon:
Free 3G Wireless – No monthly payments, no annual contracts
Global 3G Coverage
Travel the globe and still get books in under 60 seconds. Kindle uses GSM technology—the most popular mobile wireless standard - with wireless coverage in over 100 countries and territories, such as Australia, Hong Kong, Germany, Japan, Norway, Spain, South Africa, the United Kingdom, and many others. Stay in touch with news from home by having your newspaper and magazine subscriptions delivered wirelessly while you travel.