One of my co-workers, who sits in an open cubicle area outside my office, routinely lets her cell phone ring, as she sits right next to it, because she doesn't feel like answering it. This is really only made horrible by the fact that she has this loud, obnoxious, repetitive ring and her voicemail only picks up after 6 or more reps.
Screw being nice to office workers.
My boss has the song "werewolves of london" as his ring tone and often lets it ring like 5 times so he can hear the fucking song.