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 dialled.
Source code coming soon.
In the meantime, get it from the app store.
Any queries, contact the author; make sure to include your email address!
Or go home.
Update 2010-02-01
Apologies for the extaordinary length of time it has taken to get an update. However, as a result of some extremely helpful feedback, I have a new version of the DTMF decoder that replaces the goertzal code with multiple band-pass filters. Essentially this means it'll work in the sort of conditions people were expecting e.g. high background noise. Bear with me and the update will be released RSN together with the source (under GPLv3). Thank you for your patience.
Update 2009-03-04
Thanks for the feedback people. If you haven't given me any feedback but have an opinon, then please pass it on. There will be an update coming soon that should make the app more useful and flexible.