At first, two iron wires connected each pair of telephones. Then switchboards brought phone wires into one location. Other inventions - the vacuum tube to amplify sound, and coaxial cables to link long distances on land and under the seas -- greatly expanded phone service. Transistors replaced the old vacuum tubes, and by the 1960s communications satellites eliminated the necessity of landlines. Today, bundles of glass fibers carry calls on laser beams of light.
Transistors replaced the old vacuum tubes