Overview: this is the most popular Java MP3 player for Motorola E398. It have ability for managing playlists (something missing in the 373 firmwares compared to the stock 372 in the default sound player) and also it have the great option for configuring custom skins. It fully supports the ROKR filesystem.

When you start the application first you need to configure your folders by going to Menu > Folders. By default you will use only the /b/mobile/audio and it's subfolders since it is your Trans Flash card where you usually store your MP3 files (who uses the 8MB phone memory for MP3?). Of course you will need to add all subfolders too (if any).
After that you will notice that all of your MP3 files will show up on your screen. Now it is the time to create your playlists. By deleting songs in the main screen you can configure the list as you like it to show as playlist (do not worry - that does not delete the actual file!). Then go to Menu > Playlists and save it.

Another option that you will most probably need to pay attention is the Menu > Types option where you can add/delete media filetypes!

LightPlayer v635 - a very good MP3 player (Russian)