Once the books are downloaded, sure.
The Kindle uses Sprint's wireless network to connect and retrieve books. I assume you would do this on the ground? Once the book is retrieved, it is stored on flash memory in your Kindle and no connection is needed.
I don't *think* you could connect to the Sprint network while flying, so I don't think you could download new stuff while you are flying, but as a very, very infrequent flyer I'll defer to the expertise of others on that.
If you're concerned about it causing interference, you can turn the wireless connection completely off with a couple of clicks. With the wireless connection off, the Kindle uses virtually no electricity. It only uses energy when you turn the page.
If you don't have a connection to the Sprint network, you can download books via your computer. So I guess if you're on a plane with your computer and the airline is providing Wifi, you can get books that way. No samples are available via computer, though.
Hope this helps!