free download PNG images :Phone

Telephone is a kind of telecommunication equipment, which allows two or more users to talk when they are too far away to hear directly. The telephone converts sound (usually the most effective human voice) into electronic signals suitable for long-distance transmission through cables or other transmission media, and plays back such signals to users in an audible form at the same time.

The first phone connects directly from one customer's office or home to another customer's location. These systems are not limited to a small number of customers, so they are quickly replaced by manually operated centralized distribution boards. This resulted in land-line telephone services, each of which was connected to the local central office switching system through a pair of dedicated lines, which had developed into a fully automatic system since the early 1900s. In order to improve mobility, from the 1930s to the mid-1900s, various radio systems have been developed for transmission between mobile customer stations on ships and cars. Motorola has launched the first handset for personal service since 1973.

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