I can plug my iPhone into my TF101 and Gallery pops up to view my pics. But, that's it. Some phones do this, some do not. If your phone has a USB Mass Storage Mode and your tablet has a USB port, it should work to view all content.
For music, I highly suggest getting into Google Music (https://play.google.com/music/listen). I have this set up and have my 15,000 songs in the Google Cloud and I can sync them any time my tablet is online, and make albums, artists, songs, playlists available offline (so long as you have free space on your tablet or phone).