We think this is a joke, but we're actually more afraid that it's not. San Francisco-based "conceptual artist" Jonathon Keats has generously offered his latest composition, "My Cage," free of charge as a ringtone through mobile multimedia vendor Start Mobile. But wait, there's a catch, it's four minutes and thirty three seconds of pure silence. And it's not the kind of silence teens can hear, either -- it's actually pure silence. So pure, in fact, that Start Mobile keenly points out that "the silence may take place without the listener being aware of it." While we think it really doesn't serve the intended function of a ringtone in the purest sense of the word, we can't argue with the price: free. Let us know in comments what percentage of calls you manage to answer, mkay?