Audio oscilloscopes for iPhone

iOscilloscope displays the iPhone’s mic in as waveform with fast fourier transform or Sonogram modes – iOscilloscope

For a more advanced view check out SignalScope –

• Analyze signals coming from the iPhone’s built-in or headset microphone, or from the built-in accelerometer.
• Zoom in or out on spectrum and waveform displays with two-finger expand/pinch gestures, even while the analyzer is running.
• Pan vertically or horizontally in zoomed displays with two-finger scrolling.
• Pinpoint individual sample values or frequencies with a cursor.
• Save high-resolution spectrum or waveform display images to the iPhone’s Camera Roll photo album.

– SignalScope

Sorry, no hardware BNC connector for iPhone as of yet ;)