1. Activate the "Automatic Answer" in the headset profile of your cell phone and set the ringing volume to "Mute"
2. Short-circuit the left middle and right pins on the bottom of the mobile phone with all connections touching each other this will activate profile "Headset".
If you cant do this just keep your earphone connected to mobile.
3. Now place it under a table in a room and call it. Now you can use your phone for checking out what people are talking about in a room. Just call on your phone.
4. The phone receives the call without ringing and you can listen to what people are saying.