Fake background noise. Newscientist reports on SoundCover which can “add artificial traffic and road works to a call at the press of a button on the mobile phone. It can mimic a thunderstorm, the dentists drill or even a circus during a call.”The software can also be used to create the sound of another phone ringing which provides an excuse for cutting off a call.
Cell phone software creates bogus backgrounds [Smart Mobs]