<Li> 1946: Bell Labs develops the germanium point - contact transistor </Li> <Li> 1947: December, W. Rae Young and Douglas H. Ring, Bell Labs engineers, proposed hexagonal cells for provisioning of mobile telephone service . </Li> <Li> 1948: Phil Porter, a Bell Labs engineer, proposed that cell towers be at the corners of the hexagons rather than the centers and have directional antennas pointing in 3 directions . </Li> <Li> 1950: The Western Electric Type 500 telephone becomes available in the United States after announcement in 1949 . </Li>

When did the telephone became a household item