A telephone call, phone call, voice call, or simply a call, is the use of a connection over a telephone network between two parties for audio communication. To start a call, the calling party, the caller, opens a connection for a particular phone number and waits for an answer to the request, often indicated by an audible ringtone. To answer the call, the called party accepts the request to start a conversation. A party is most commonly a single person, but can be a group of people (i.e. conference call) or a machine (i.e. fax). In some contexts, the term A-Number refers to the caller and B-Number refers to the called party. The telephone call was enabled by multiple inventions in the mid- to late-19th century including the telephone. Initial technology involved point-to-point electrical wire connections between telephone installations, until centralized exchanges evolved where telephone operators established each interconnection manually at a telephone switchboard after asking the calling party for their call destination. After the invention of automatic telephone exchanges in the 1890s, the process became increasingly automated, eventually leading to the widespread adoption of digital exchanges in the second half of the 20th century, including the transition to wireless communication via mobile telephone networks and cellular networks. With the development of the Internet, the cost of telephone calls was drastically reduced with Voice over Internet Protocol (VoIP).
First telephone call It is generally believed that the first telephone call was on March 10, 1876, when Alexander Graham Bell said, “Mr. Watson – Come here – I want to see you.” However, there are two other candidates for this credit, and wiich of the three candidates deserves credit depends on some details. The first test with promising results was in June 1875 when Bell and his assistant, Thomas Watson, tested the so-called gallows telephone. Its transmitter utilized Bell’s novel concept of vibrating a magnetized part in front of a coil of wire to create an electric current according to the principle of Faraday’s law. This telephone transmitted voice-like sounds (timbre) consisting of many frequencies, and Watson declared that “The gods had arrived.” But distinct words were not heard as had been expected. The second test with improved results was in March 1876, and that was the test in which Bell literally shouted, “Mr. Watson – Come here – I want to see you.” Although Watson claimed to have heard those words via telephone, Bell astutely tried to confirm Watson’s claim by changing rooms and having Watson read unfamiliar pages from a book. Bell then wrote “It was certainly the case that articulate sounds proceeded from S [the receiver]. The effect was loud but indistinct and muffled.” Bell further noted “As it was I could not make out the sense – but an occasional word here and there was quite distinct.” Nevertheless, with reference to those words, in 1916 Bell unveiled a plaque in Boston that reads, “Here Alexander Graham Bell transmitted to Thomas Augustus Watson the first complete and intelligible sentence by telephone March 10, 1876.” For those tests in March 1876, Bell used a liquid transmitter that appears to be like the one designed by Elisha Gray, Bell’s competitor. It varied the resistance in a battery circuit and was nothing like Bell’s vibrating magnet design. Gray never successfully demonstrated his liquid transmitter, and it was not developed into a practical instrument. Further, Bernard Finn, whose department at the Smithsonian holds Bell’s artifacts, said that Gray’s design “was in fact worthless.” The third test with successful results was conducted on May 22, 1876, when Edward Wilson was substituting for Watson. Using Bell’s vibrating-magnet design, Bell said “I could hear very distinctively the sounds that were uttered into A [the transmitter’s mouthpiece]. Consonants & vowels were equally intelligible. Although my ear was pressed tightly against S’ [the receiver] – I heard the sentence ‘Mr. Bell are you going to the Centennial’ with the utmost distinctiveness.” This was soon confirmed at the 1876 Centennial Exhibition by demonstrations in front of many witnesses. Further improvements were made to Bell’s vibrating magnet telephone in November 1876, and the improved design was patented and became the world’s first commercial telephone.
Information transmission A telephone call may carry ordinary voice transmission using a telephone, data transmission when the calling party and called party are using modems, or facsimile transmission when they are using fax machines. The call may use land line, mobile phone, satellite phone or any combination thereof. When a telephone call has more than one called party it is referred to as a conference call. When two or more users of the network are sharing the same physical line, it is called a party line or Rural phone line.
If the caller's wired phone is connected directly to the calling party, when the caller takes their telephone off-hook, the calling party's phone will ring. This is called a [hot line] or [ringdown]. Otherwise, the calling party is usually given a tone to indicate they should begin dialing the desired number. In some (now very rare) cases, if the calling party cannot dial calls directly, they will be connected to an operator who places the call for them. Calls may be placed through a public network, such as the public switched telephone network (PSTN), provided by a commercial telephone company or a private network, such as a private branch exchange (PBX). In most cases a private network is connected to the public network to provide PBX users with access to the larger networks. Incoming calls to a private network arrive at the PBX in two ways: either directly to a users phone using direct inward dialing or indirectly via a human or electronic receptionist who will answer the call and connect it to the desired user. Most telephone calls through the PSTN are set up using ISUP signalling messages or one of its variants between telephone exchanges to establish the end to end connection. Calls through PBX networks are set up using QSIG, DPNSS or variants.
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