How is it possible that you are calling another phone?

Answer

All sound, including when you speak, is actually vibrations that move through the air. (For example, this is why some opera singers can break glass when they sing very high and forcefully.) A telephone contains a microphone and a small loudspeaker. The microphone converts vibrations from the air into electrical vibrations that then reach the telephone of the person you are calling via the telephone network. There, the loudspeaker converts the electrical vibrations back into sound. Because you both have a microphone and speaker in your phone, you can talk to each other.