Completely redesigned decoder!
Turns your iPhone into a simple DTMF decoder. Simply hold the iPhone's microphone near to a clear source of DTMF tones (telephone "Touch Tones") and it will display the numbers being dialed. The decoded digits are also placed into a text area from which you can copy them to the clipboard.
A row of LEDs indicate which frequencies are present in the signal - each LED corresponds to a single frequency.
See it in action here:
Source code freely available: