Phone Incoming Call Flasher

This is a circuit of phone message flasher, an alternative way to get alarmed when there is an incoming call. When the phone rings, high line voltage will be detected by A differential amplifier with hysteresis (Q2, Q3, and Q1). This action will turn on multivibrator Q5/Q6, Q4. The LED will flashed via Q7. When the phone line voltage drops to less then 9V, the Q2 and Q1 will be turned off, which indicates an off hook condition. Here is the schematic diagram of the circuit: