Telephones:

It was Philipp Reis, a German physicist, an inventor and a school teacher the first to come up with the idea of the telephone.  He discovered that with the electric connections between the "conversion of sound vibrations and electric impulses", a machine that could generate sounds of voices across wires was developed in 1860.  He put them in some of the classrooms and listened in on the students in which the students knew nothing of.  Unfortunately, he faced a slight problem.  He found out that to send sounds, breakage of the first diaphragm should not happen, which will affect the electricity flow tot he second that should vary.  however, Reis' diaphragm drive a thin rod to changing depths in an electric coil but neither did it make or break the current.

Alexander Graham Bell faced the same trouble.  After some thought that he got form an American inventor, Elisha Gray, he tried a diaphragm-driven needle with a water/acid solution which created the continuous variable resistance and electrical current he wanted.  However, evaporation and immobility caused the failure.  A highlight to this process happened in June, 1875.  Thomas Watson was asked to "pluck a steel receiver reed with his finger to make sure that it was not stuck."  When he moved the reed, the receiver in Bell's room also did, even though the current was off.  An "undulating current" was produced and served as the main component of the magnetic field in the invention.  The telephone is then functioning.  The great day came to both of them was 12 March 1876.  The first message "Mr. Watson --come here-- I want to see you" was transmitted from Bell to Watson, through the telephone.

So how does it really work?

a telephone is one of the simplest devices you have in your house. It is so simple because the telephone connection to your house has not changed in nearly a century. If you have an antique phone from the 1920s, you could connect it to the wall jack in your house and it would work fine!

The very simplest working telephone would look like this inside:

As you can see, it only contains 3 parts and they are all simple:

• A switch to connect and disconnect the phone from the network. This switch is generally called the hook switch. It connects when you lift the handset.
• A speaker, which is generally a little 50 cent 8-ohm speaker of some sort
• A microphone. In the past, telephone microphones have been as simple as 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.
That's it! You can dial this simple phone by rapidly tapping the hook switch - all telephone switches still recognize "pulse dialing" like this. If you pick the phone up and rapidly tap the switch hook 4 times, the phone company's switch will understand that you have dialed a 4, for example.

The only problem with the phone shown above is that when you talk you will hear your voice through the speaker. Most people find that annoying, so any real phone contains a device called a duplex coil or something functionally equivalent to block the sound of your own voice from reaching your ear. A modern telephone also includes a bell so it can ring and a touch-tone keypad and frequency generator. A "real" phone looks like this:

Still, it's pretty simple! In a modern phone there is an electronic microphone, amplifier and circuit to replace the carbon granules and loading coil. The mechanical bell is often replaced by a speaker and a circuit to generate a pleasant ringing tone.