This Shield is a Dual-Tone Multi-Frequency signaling module decoder for Arduino With it's audio connector you can decode the crazy funny noises common phones make. If you are not sure what I'm talking about, imagine a home phone while pressing several of its keys. These Touch-Tones have a specific frequency or sound that this module can decode. This Shield is a Audio code system that will allow you to send commands to your Arduino via Audio signal.
Together with GMS / GPRS / GPS shield this module can communicate your Arduino with any phone land line or Cell phone in the world, within GSM signal range. Which goes as far as your cellphone.