actually Amazon has contracts with mobile-internet providers almost worldwide to deliver the books
via the Amazon Whispernet.
All books bought in the Kindle store should be a free download via 3G (or slower connection depending on location).
But if you have set up some subscriptions like magazines and newspapers or forwarding like Instapaper, Amazon will charge you for the use of the 3G network outside the US.
Here's a link
, read it carefully and you should be ok!
is the coverage map for the Whispernet worldwide and US