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The microphone converts the sound waves to electrical signs and then these are sent through the telephone network to the other phone and there modified by an earphone, or speaker,chuyen nha gia re back into sound waves. Telephones are a duplex communications medium, meaning they allow the people on both ends to talk simultaneously. The telephone network, consisting of a worldwide net of telephone lines, fiberoptic cables, microwave transmission, cellular networks, communications satellites, and undersea telephone cables connected by switching centers, allows any telephone in the world to communicate with any other. Each telephone line has an identifying number called its telephone number. To initiate a telephone call the user enters the other telephone's number into a numeric key pad on the phone. Graphic symbols used to help designate telephone service or phone-related information in print, signage, and other media include .dich vu chuyen van phong

Although originally designed for simple voice communications, most modern telephones have many additional capabilities.chuyen nha tron goi They may be able to record spoken messages, send and receive text messages, take and display photographs or video, play music, and surf the Internet. A current trend is phones that integrate all mobile communication and computing needs; these are called smartphones. chuyen van phong