*NOTE: this Thing is designed for printing on a non-shrinking printer (ie through Shapeways, etc). For a MakerBot-friendly, earlier version, see:
A friction-fit cap for the bottom of the iPhone 4/5 that allows a stethoscope to be attached and recorded using the built-in microphone.
As the sound passes through the rubber stethoscope tubing, it is funneled directly to the mic at the bottom of the phone.
A quick test recording can be heard here: