Conceptual artist Johnaton Keats has released a cell-phone ring tone cover of the legendary 4' 33'' by John Cage. 4' 33'' consists of three movements, which are actually the conductor turning the pages, and 273 seconds of silence, a reference to -273 degrees - Absolute Zero . The idea is that the audience are actually both creating the piece by making sounds, and are listening to the piece, so that each performance is unique. Cage was influenced by a series of blank paintings by Robert Rauschenberg, where different light conditions and the shadow of the observer created unique paintings for each observer.
Here is an interesting symphonic version of 4' 33'' from BBC. Note how the audience tries to be silent, but fails to do so when the conductor turns the pages.