dTunes offering something that the iPod player does'nt, is direct access to music ad video download sites. You can download music, video or even torrents directly to your iPhone.
dTunes stores downloaded MP3 tracks in /var/mobile/Library/Downloads and shows a list of files in that directory and lets you play the songs or delete them as well.
you must have a jailbroken iPhone in order to download dTunes. Did you know, Apple has not approved this application because it duplicates a current iPhone feature.
So, Use it at your own risk!