I could download items from my Kindle version 4.1.3 wirelessly, turning off Aeroplane Mode as instructed. I did so for about 250 titles over several years. Now, this "Whispernet" service does not work, either for new items or to restore deleted items from the archive, although I get billed for the new items (but get refunds easily enough).
Can anyone suggest a remedy? I can't find a suitable way into Amazon to raise this, "Kindle Support" having no relevant handle. From way back, I recall some kind of reset which involved pressing own the Start key and holding for 40 seconds but that makes no difference.