Dreadtech iOS DTMF Decorder
Turns your iPhone into a simple DTMF decoder. Simply hold the iPhone's microphone near to a source of DTMF tones (telephone "Touch Tones") and it will display the numbers being dialed. Version 1.8 not only has a far superior decoding engine, but it also allows you to tweak the sensitivity. You may copy the decoded digits to the clipboard from the text area.
Available in the App Store: https://itunes.apple.com/us/app/dtmf-decoder/id306195275