How to download music straight to your iphones itunes? (jailbroken) (no computer)?

I have a jailbroken iphone 4 and, i want to download songs from youtube straight to my phones ipod, is there any cydia app to do so?
The reason for this is because i want to make a ringtone from a youtube song but can't unless the song is in my phones itunes. Unless you know a way i can?

Search Free MP3 in the app store there's one that's emblem is blue says mp3 and has a musical note go to the browser button and up top go to mp3skull.com