Telephone call in the context of "Rotary dial"

A telephone number is the address of a telecommunication endpoint, such as a telephone, in a telephone network, such as the public switched telephone network (PSTN). A telephone number typically consists of a sequence of digits, but historically letters were also used in connection with telephone exchange names.

Telephone numbers facilitate the switching and routing of calls using a system of destination code routing. Telephone numbers are entered or dialed by a calling party on the originating telephone set, which transmits the sequence of digits in the process of signaling to a telephone exchange. The exchange completes the call either to another locally connected subscriber or via the PSTN to the called party. Telephone numbers are assigned within the framework of a national or regional telephone numbering plan to subscribers by telephone service operators, which may be commercial entities, state-controlled administrations, or other telecommunication industry associations.

A mobile phone or cell phone is a portable wireless telephone that allows users to make and receive calls over a radio frequency link while moving within a designated telephone service area, unlike fixed-location phones (landline phones). This radio frequency link connects to the switching systems of a mobile phone operator, providing access to the public switched telephone network (PSTN). Modern mobile telephony relies on a cellular network architecture, which is why mobile phones are often referred to as 'cell phones' in North America.

Beyond traditional voice communication, digital mobile phones have evolved to support a wide range of additional services. These include text messaging, multimedia messaging, email, and internet access (via LTE, 5G NR or Wi-Fi), as well as short-range wireless technologies like Bluetooth, infrared, and ultra-wideband (UWB).

In telecommunications and computer networking, multiplexing (sometimes contracted to muxing) is a method by which multiple analog or digital signals are combined into one signal over a shared medium. The aim is to share a scarce resource—a physical transmission medium. For example, in telecommunications, several telephone calls may be carried using one wire. Multiplexing originated in telegraphy in the 1870s, and is now widely applied in communications. In telephony, George Owen Squier is credited with the development of telephone carrier multiplexing in 1910.

The multiplexed signal is transmitted over a communication channel such as a cable. The multiplexing divides the capacity of the communication channel into several logical channels, one for each message signal or data stream to be transferred. A reverse process, known as demultiplexing, extracts the original channels on the receiver end.

A telephone network is a telecommunications network that connects telephones to support calls between them that facilitate human communication. The technology eventually came to be used for communication between humans and machines (i.e. fax and dial-up Internet access) although today this has been replaced with digital technologies.

The world was transformed in the 1920s as the phone became ubiquitous; with people sharing news, ideas, and personal information. During the 1990s, the phone helped transform the world again with the advent of computers, sophisticated communication devices, and via dial-up internet.

A VoIP phone or IP phone uses voice over IP technologies for placing and transmitting telephone calls over an IP network, such as the Internet. This is in contrast to a standard phone which uses the traditional public switched telephone network (PSTN).

Digital IP-based telephone service uses control protocols such as the Session Initiation Protocol (SIP), Skinny Client Control Protocol (SCCP) or various other proprietary protocols.

Mobile telephony is the provision of wireless telephone services to mobile phones, distinguishing it from fixed-location telephony provided via landline phones. Traditionally, telephony specifically refers to voice communication, though the distinction has become less clear with the integration of additional features such as text messaging and data services.

Modern mobile phones connect to a terrestrial cellular network of base stations (commonly referred to as cell sites), using radio waves to facilitate communication. Satellite phones use wireless links to orbiting satellites, providing an alternative in areas lacking local terrestrial communication infrastructure, such as landline and cellular networks. Cellular networks, satellite networks, and landline systems are all linked to the public switched telephone network (PSTN), enabling calls to be made to and from nearly any telephone worldwide.

The telecommunications industry within the sector of information and communication technology comprises all telecommunication/telephone companies and Internet service providers, and plays a crucial role in the evolution of mobile communications and the information society.

Telephone calls continue to be the industry's largest revenue generator, but due to advances in network technology, telecom today is less about voice and increasingly about text (messaging, email) and images (e.g. video streaming).High-speed Internet access for computer-based data applications such as broadband information services and interactive entertainment is pervasive. Digital subscriber line (DSL) is the main broadband telecom technology. The fastest growth comes from (value-added) services delivered over mobile networks.