Get PRC/Mobi Files into Kindle Apps
I can't speak to the Kindle for Blackberry app, but as to Kindle for PC and Kindle for iPhone, it's relatively easy to load your mobi/prc files (without drm) purchased elsewhere. You just need to find the folder in which the Kindle App stores books and then add yours. So, for a PC running Windows 7, the folder is /documents/My Kindle Content. On an iPhone, the folder is var/mobile/applications/kindle/ebooks. Of course, to get a file into your iphone, it's a whole lot easier if you're jailbroken (i don't know how to do it if you're not). Hope that helps.