Module for recognizing a tone or sound?

I'm thinking about my first arduino project. Right now I'm just in the research phase, so I'm hoping I can get a little help here.

My project is to a visual notifier for text messages. The best way (I believe) to do this is by taking a bluetooth headset and hooking the earpiece to arduino. When I get a text, the bluetooth headset will play a sound (or rather just a tone, this might be easier for the arduino to recognize), and the arduino will recognize it and activate an LED until I press a button to clear it.

Does anyone see a flaw in this? Would the Arduino be appropriate for this? Thanks in advance. :)

One problem i can see is that you would need to put a small microphone in front of the bluetooht earpiece to "listen" for a sound. This microphone could also pick up other noices which would trigger your LED falsly.

what about using dtmf signaling? there are ic's made specifically for decoding, and the telephone lines are not the clearest lines, so i'd imagine you could get away with some noise being picked up