I just added this early sixties film about damaged urban dwellers to my favorite films list. I relate to this movie on a visceral level--the lives of broken nonentities trying to find sanctuary is eerily familiar. If you've lived in a city, if you've wanted to die, if you've been held captive in a basement apartment by a dead-end-job alcoholic--you will relate.
It's probably not a good thing when you say, "That's it?!" as the credits roll at the end of a movie. The Sound of My Voice felt incomplete. The plot and characters weren't developed. I will grant that I was also sewing while I watched the film, but it was so slight that I'm pretty sure that I didn't miss anything revelatory. It reminded me of the TV show Lost; I don't think that the writer(s) knew the explanation of the mystery any more than the viewer(s).