I have roughly 19 gigs of music installed on my iPhone 5. However, on two occasions, nearly all of my music has been deleted -- this without even being hooked to my computer to sync. Yesterday, I was playing music just fine. This morning, all but 14 songs are gone. The albums/artists/tracks still show up in the Music app, but they don't play. My iPhone shows that I have 14 songs and the reclaimed free space to account for them.