Turns your iPhone into a simple DTMF decoder. Simply hold the iPhones 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.
See it in action here:
https://www.youtube.com/watch?v=l_QD8KFCJPw
Source code freely available:
https://github.com/veghead/ios-dtmf-decoder