This project is based in my father's project "DTMF remote control with PIC". http://www.atva.com.ar/dtmf_3dj/dtmf_3dj.htm (spanish) Since I haven't time to work with PICs, I ported the project to AVR using an Atmega328p with Arduino bootloader.
This project is very similar to my father's one, because the working method is the same. We use a DTMF decoder like MT8870 or HT9170 (compatible pin to pin) to decode the analog audio signal and 'extract' the dtmf codes and convert it to a digital binary signal.
That binary signal is easily interpreted by an Arduino, after that I parse it storing the received signals into an array to command some outputs.
This is the github project: https://github.com/masterl1nk/DTMFDuino
Here is the schematic circuit: And a video: http://www.youtube.com/watch?v=fz7CHktLppE
Sorry for my english!
Greetings from Argentina