I have used moby explorer on z520 and z525 and it worked good (deselect read only and be able to delete), but when I tried it on my w300 I was only able to do this with a some but not all files. It seems as if there is a hidden file system because the files I couldn't get rid of do not show up anywhere in mobyexplorer (Yes I have the option to show hidden files). It is anoying because if you set the walkman to play all files, you end up with some predefined ringtones in your playlist. I haven't tried it yet but I think customizing the FS via Far Manager is the only way.