If you put your phone close to your amp or sound card and if they are not perfectly shielded then you can hear when the phone is transmitting the signal. You ca

If you put your phone close to your amp or sound card and if they are not perfectly shielded then you can hear when the phone is transmitting the signal. You can hear modem-like sound before receiving a call or a message, and in idle mode the phone usually transmits something every 15-30 minutes.