Alexander Graham Bell made the first telephone call on March 10, 1876, by asking his assistant to come to his room.

Bell's first telephone used a liquid transmitter to send sound. When he spoke, his voice made a thin sheet called a diaphragm vibrate. This vibration moved a needle in a cup of water mixed with acid. The movement changed how much electricity flowed through the wire.The receiver at the other end turned the electricity back into sound waves. This allowed Thomas Watson to hear Bell's voice from another room. Bell received U.S. Patent No. 174,465 for this invention. It is often called the most valuable patent ever created.Another inventor named Elisha Gray tried to patent a similar idea on the same day. This led to many legal arguments over who truly invented the telephone. Bell's company eventually became AT&T. By 1886, more than 150,000 people in the United States owned a telephone.Early phones were improved by Thomas Edison in 1877. He created a carbon microphone that made the sound much clearer. This allowed people to talk over longer distances. The first phone line across the entire United States was finished in 1915. It connected New York City to San Francisco.