Portal:Telephones

The National Do Not Call Registry is a database maintained by the United States federal government, listing the telephone numbers of individuals and families who have requested that telemarketers not contact them. Certain callers are required by federal law to respect this request. Separate laws and regulations apply to robocalls in the United States.

The Federal Trade Commission (FTC) opened the National Do Not Call Registry in order to comply with the Do-Not-Call Implementation Act of 2003 (Pub. L. 108–10 (text) (PDF), was H.R. 395, and codified at 15 U.S.C. § 6101 et seq.), sponsored by Representatives Billy Tauzin and John Dingell and signed into law by President George W. Bush on March 11, 2003. The law established the FTC's National Do Not Call Registry in order to facilitate compliance with the Telephone Consumer Protection Act of 1991. A guide by FTC addresses a number of cases.

Registration for the Do-Not-Call list began on June 27, 2003, and enforcement started on October 1, 2003. Since January 1, 2005, telemarketers covered by the registry have up to 31 days (initially the period was 90 days) from the date a number is registered to cease calling that number. Originally, phone numbers remained on the registry for a period of five years, but are now permanent because of the Do-Not-Call Improvement Act of 2007, effective February 2008. (Full article...)

Mobile radio telephone systems were mobile telephony systems that preceded modern cellular network technology. Since they were the predecessors of the first generation of cellular telephones, these systems are sometimes retroactively referred to as pre-cellular (or sometimes zero generation, that is, 0G) systems. Technologies used in pre-cellular systems included the Push-to-talk (PTT or manual), Mobile Telephone Service (MTS), Improved Mobile Telephone Service (IMTS), and Advanced Mobile Telephone System (AMTS) systems. These early mobile telephone systems can be distinguished from earlier closed radiotelephone systems in that they were available as a commercial service that was part of the public switched telephone network, with their own telephone numbers, rather than part of a closed network such as a police radio or taxi dispatching system.

These mobile telephones were usually mounted in cars or trucks (thus called car phones), although portable briefcase models were also made. Typically, the transceiver (transmitter-receiver) was mounted in the vehicle trunk and attached to the "head" (dial, display, and handset) mounted near the driver seat. They were sold through WCCs (Wireline Common Carriers, a.k.a. telephone companies), RCCs (Radio Common Carriers), and two-way radio dealers. (Full article...)

Example of a North American dial tone

Listen to a dial tone from North America of 350 Hz + 440 Hz.

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Example of a UK/British dial tone

Listen to a dial tone from the United Kingdom of 350 Hz + 450 Hz.

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Example of a current European dial tone

Listen to a European dial tone of 425 Hz

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Example of a French dial tone

Listen to a French dial tone of 440 Hz

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Example of a Japanese dial tone

Listen to a Japanese dial tone of 400 Hz

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A dial tone (dialling tone in the UK) is a telephony signal sent by a telephone exchange or private branch exchange (PBX) to a terminating device, such as a telephone, when an off-hook condition is detected. It indicates that the exchange is working and is ready to initiate a telephone call. The tone stops when the first dialed digit is recognized. If no digits are forthcoming, the partial dial procedure is invoked, often eliciting a special information tone and an intercept message, followed by the off-hook tone, requiring the caller to hang up and redial. (Full article...)

Elisha Gray (August 2, 1835 – January 21, 1901) was an American electrical engineer who co-founded the Western Electric Manufacturing Company. Gray is best known for his development of a telephone prototype in 1876 in Highland Park, Illinois. Some recent authors have argued that Gray should be considered the true inventor of the telephone because Alexander Graham Bell allegedly stole the idea of the liquid transmitter from him. Although Gray had been using liquid transmitters in his telephone experiments for more than two years previously, Bell's telephone patent was upheld in numerous court decisions.

Gray is also considered to be the father of the modern music synthesizer, and was granted over 70 patents for his inventions. He was one of the founders of Graybar, purchasing a controlling interest in the company shortly after its inception. (Full article...)