Controlling ard. via cell phone using headphones(?)


I'd like to let my arduino "sense" incoming calls on my cell phone, I know there are a lot of ways, but I thought of this very rude one and I'd like to know what you think about it. Essentially, I link headphones to my phones, I can work on the cell settings so that when a call arrives the sound comes off the headphones and not the phone's speaker. So If i cut off the one of the headphones' speaker and pull out the wires I have an input voltage controlled via phone, right? I know this must be a very rude and inelegant way, but do you think it could work? I've tried but I'm stuck in a silly proble, I don't get what's inside the headphones' wire, I can't find the conducting wires :(