Non DRM Mobipocket format is already supported on the Kindle - just drag and drop.
Non-DRM Mobi books, like free e-books found online in Mobi format, or files you convert to Mobi files, are already supported on Kindle.
Typically ebook readers are larger than PMP's with larger screens. If you're going to read for a few hours, then the screen of a typical PMP becomes pretty eye-straining (due to size, contrast, and brightness).
DRM is not to prevent other files from being readable on the Kindle.
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