page_title: History of the telephone
section_title: 20th-century developments
hierarchical_section_title: History of the telephone / 20th-century developments
caption_attribution_description: Top of cellular transmitting tower in the United States
context_page_description: This history of the telephone chronicles the development of the electrical telephone, and includes a brief review of its predecessors.
context_section_description: By 1904, over three million phones in the U.S. were connected by manual switchboard exchanges. By 1914, the U.S. was the world leader in telephone density and had more than twice the teledensity of Sweden, New Zealand, Switzerland, and Norway. The relatively good performance of the U.S. occurred despite competing telephone networks not interconnecting. On January 6, 1927, W. S. Gifford, president of the American Telephone & Telegraph Company, called Evelyn P. Murray to test the first commercial telephone line across the Atlantic Ocean.
  What turned out to be the most popular and longest-lasting physical style of telephone was introduced in the early 20th century, including Bell's model 102 telephone. A carbon granule transmitter and electromagnetic receiver were united in a single molded plastic handle, which when not in use were placed in a cradle in the base unit. The circuit diagram of the model 102 shows the direct connection of the receiver to the line, while the transmitter was induction coupled, with energy supplied by a local battery. The coupling transformer, battery, and ringer were in a separate enclosure from the desk set. The rotary dial in the base interrupted the line current by repeatedly but very briefly disconnecting the line 1 to 10 times for each digit, and the hook switch (in the center of the circuit diagram) permanently disconnected the line and the transmitter battery while the handset was on the cradle.
  Starting in the 1930s, the base of the telephone also enclosed its bell and induction coil, obviating the need for a separate ringer box. Power was supplied to each subscriber line by central-office batteries instead of the user's local battery, which required periodic service. For the next half century, the network behind the telephone grew progressively larger and much more efficient, and, after the rotary dial was added, the instrument itself changed little until Touch-Tone signaling started replacing the rotary dial in the 1960s.
  The history of mobile phones can be traced back to two-way radios permanently installed in vehicles such as taxicabs, police cruisers, railroad trains, and the like. Later versions such as the so-called transportables or "bag phones" were equipped with a cigarette-lighter plug so that they could also be carried, and thus could be used as either mobile two-way radios or as portable phones by being patched into the telephone network.
  In December 1947, Bell Labs engineers Douglas H. Ring and W. Rae Young proposed hexagonal cell transmissions for mobile phones. Philip T. Porter, also of Bell Labs, proposed that the cell towers be at the corners of the hexagons rather than the centers and have directional antennas that would transmit/receive in 3 directions (see picture at right) into 3 adjacent hexagon cells. The technology did not exist then and the radio frequencies had not yet been allocated. Cellular technology was undeveloped until the 1960s, when Richard H. Frenkiel and Joel S. Engel of Bell Labs developed the electronics.
  Meanwhile, the 1956 inauguration of the TAT-1 cable and later international direct dialing were important steps in putting together the various continental telephone networks into a global network.
  On 3 April 1973, Motorola manager Martin Cooper placed a cellular-phone call (in front of reporters) to Dr. Joel S. Engel, head of research at AT&T's Bell Labs. This began the era of the handheld cellular-mobile phone.
  Cable-television companies began to use their fast-developing cable networks with ducting under the streets of the United Kingdom in the late 1980s to provide telephony services in association with major telephone companies. One of the early cable operators in the UK, Cable London, connected its first cable telephone customer in about 1990.
caption: Top of cellular telephone tower
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