Go plug out the telephone line of the reciver for a second.That wod be just as she hang up.Or if you like building enectronic things Build an litle timer that you wod conect betwen the phone and the phone line.So that a rele or a transistor wod disconect and reconect reconect the phone line wean a certan amaunt of time has pased from the start of the call call.But it wod be dificult to make it not work for incoming calls.Meaby the ring pusle wod triger a flip flop wich disables the circuit and wean it hangs up the flip flop wod reset.