Escape pod is an application with one purpose -- to get you out of phone calls. The idea is simple, and except for hardware constraints, it's well done.
The idea is that if you are on a phone call you want to get out of you launch Escape Pod, select a sound, and touch the escape pod on screen to play the sound. The included sounds are things like a baby crying, doorbell, etc. Hopefully that sound and a good job of verbal maneuvering will get you off the phone call.
The only real problem with this is the iPhone hardware issues. When you are on a call, the sound from this app only plays through the ear piece. While this can be picked up by the microphone, it's really quiet even when turned up all the way. That said, the caller can still hear it unless you are in an already loud location -- it just sounds muted. Perhaps this sounds more realistic anyway?
Update 10/2: as pointed out by the developer in the comments below, you can also use this with the speakerphone turned on. This makes a huge difference in the volume and makes it much easier to hear by the person on the other end of the call. Thanks for pointing this out! Rating increased.If you are the kind of person who has the need to get out of a phone calls, this might be helpful. If you are cheap, you could always use the going out of cell range lie.