Originally Posted by tradewinds
I got tired of all the manual steps, so wrote a little os x application to help me extract the mobi ebooks I've purchased using the iphone kindle app. Hope this helps someone else. Basically, it scans your iphone backup directory for mobi files, and decrypts them to a directory of your choice. You just have to add your iphone ID which you can get from itunes by clicking on serial # on Summary page for your iphone. Once extracted, you can then drag the mobi file into calibre.
search github for TradeWinds, dmg available on downloads tab
What language did you write this application in? If you use Python or Pearl, it could then be cross platform compatible and also work on Windows.