The best input formats are taken directly from MiniDV cameras, and HDV cameras. Anything else may or may not work. MPEG2 video has gotten better but it isn't perfect.
The support for the P2 media will be available soon.
Other than that, Premiere Pro isn't designed to work with cell phone cameras, media imported from the Internet, or any other consumer formats. To import some professional formats, you may need an SDI card.