Phone that works in nature

It might be one of the simplest devices thats become a part of our lives. But the design and working of a telephone is not known to everyone. Its a simple instrument which can be comprehended by anyone.As you can see, it contains three parts and they are all simple:
A switch to connect and disconnect the phone from the network. The switch is generally called the Hook Switch. It connects when you lift the handset.A Speaker.A Microphone - Carbon granules compressed between two thin metal plates. Sound waves from your voice compress and decompress the granules, changing the resistance of the granules and modulating the current flowing through the microphone.The dialling from this simple phone is very easy by rapidly tapping the hook switch. If you pick up and rapidly tap the switch hook four times, the phone company's switch will recognise that you have dialled a "4".Now how does two people gets connected through a telephone? The following are the steps involved:The signal leaves your house to a telephone box outside.The local exchange is connected to all the phones in a small geographical area.From the local exchanges, calls are routed to the main exchange.The main exchange may route the call to another main exchange and the reverse process follows.