I am confused as to why the author of the book paying for the download of the end user in the first place? If the end user decides to download it via 3G it should either come out of their existing data allowance or be billed to their phone bill...
... or alternatively they can download it over Wifi and neither the end user, Amazon or the author should pay for it?
What you're missing is that the kindles' 3G is not paid for by the user. It's free and comes with international roaming, something that carriers tend to charge an arm and a leg for.
... or alternatively they can download it over Wifi and neither the end user, Amazon or the author should pay for it?