Vertical service code

The asteriskos used in an early Greek papyrus.

Sequence of digits and the signals star (*) and number sign (#) dialed on a telephone keypad vertical service code or rotary dial to enable or disable certain telephone service features.

- Vertical service code
The asteriskos used in an early Greek papyrus.

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The keypads on telephones for the Autovon systems used all 16 DTMF signals. The red keys in the fourth column produce the A, B, C, and D DTMF events. In this case the letters indicate the precedence (urgency) of the call; (from lowest (at the bottom) to highest; Priority, Immediate, Flash or Flash Override

Dual-tone multi-frequency signaling

Telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centers.

Telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centers.

The keypads on telephones for the Autovon systems used all 16 DTMF signals. The red keys in the fourth column produce the A, B, C, and D DTMF events. In this case the letters indicate the precedence (urgency) of the call; (from lowest (at the bottom) to highest; Priority, Immediate, Flash or Flash Override
DTMF keypad layout.
Combination of 1209 Hz and 697 Hz sine waves, representing DTMF "1"
Two CMD CM8870CSI DTMF Receivers

This led to the addition of the number sign octothorpe asterisk or "star" (*) keys as well as a group of keys for menu selection: A, B, C and D. In the end, the lettered keys were dropped from most phones, and it was many years before the two symbol keys became widely used for vertical service codes such as *67 in the United States of America and Canada to suppress caller ID.

A telephone keypad using the ITU E 1.161 International Standard.

Telephone keypad

Keypad installed on a push-button telephone or similar telecommunication device for dialing a telephone number.

Keypad installed on a push-button telephone or similar telecommunication device for dialing a telephone number.

A telephone keypad using the ITU E 1.161 International Standard.
Telephone with letters on its rotary dial (1950s, UK)
British GPO 726 telephone of 1967.
A standard telephone keypad.
The official toll-free hotline for the California Department of Transportation's Adopt-a-Highway program is 1-866-236-7824, but signs advertise the number as 1-866-ADOPTAHWY, with two extra digits, for memorability.
Mobile phone keypad with Latin and Japanese letters.

These keys were added to provide signals for anticipated data entry purposes in business applications, but found use in Custom Calling Services (CLASS) features installed in electronic switching systems.

A Swiss rotary telephone dial from the 1970s, showing the telephone's number (94 29 68) along with those of various local emergency services

Telephone number

Sequence of digits assigned to a fixed-line telephone subscriber station connected to a telephone line or to a wireless electronic telephony device, such as a radio telephone or a mobile telephone, or to other devices for data transmission via the public switched telephone network or other public and private networks.

Sequence of digits assigned to a fixed-line telephone subscriber station connected to a telephone line or to a wireless electronic telephony device, such as a radio telephone or a mobile telephone, or to other devices for data transmission via the public switched telephone network or other public and private networks.

A Swiss rotary telephone dial from the 1970s, showing the telephone's number (94 29 68) along with those of various local emergency services
Telephone numbers for sale in Hong Kong.
A business card from Richard Nixon's first Congressional campaign in 1946; his phone number can be seen as "Whittier 42635"
Face of a 1939 rotary dial showing a 2L-4N style alphanumeric telephone number LA-2697.
2008 photo shows a hairdressing shop in Toronto with an exterior sign showing the shop's telephone number in the old two-letters plus five-digits format.
Modern telephone keypad contains "*" and "#"

Telephone numbers are often dialed in conjunction with other signaling code sequences, such as vertical service codes, to invoke special telephone service features.

The asteriskos used in an early Greek papyrus.

Asterisk

Typographical symbol.

Typographical symbol.

The asteriskos used in an early Greek papyrus.
Early asterisks seen in the margin of Greek papyrus.
The Star of Life may represent emergency medical services
Asterisks used to illustrate a section break in Alice's Adventures in Wonderland

) They are used to navigate menus in systems such as voice mail, or in vertical service codes.

NTT Communications trade mark for free dial, often used in print advertising.

Toll-free telephone number

Telephone number that is billed for all arriving calls instead of incurring charges to the originating telephone subscriber.

Telephone number that is billed for all arriving calls instead of incurring charges to the originating telephone subscriber.

NTT Communications trade mark for free dial, often used in print advertising.

There are a few special mobile-only numbers (like *CAA to call the Canadian Automobile Association) which are free from cell phones, these are actually vertical service codes.

The asteriskos used in an early Greek papyrus.

Automatic callback

The asteriskos used in an early Greek papyrus.

In telecommunication, an automatic callback is a computer telephony calling feature that permits a user, when encountering a busy condition or other condition where the called individual is unavailable, to instruct the system to retain the called number and to establish the call when there is an available line or when the called number is no longer busy.

Common physical security access control with a finger print.

Access control

Selective restriction of access to a place or other resource, while access management describes the process.

Selective restriction of access to a place or other resource, while access management describes the process.

Common physical security access control with a finger print.
A sailor checks an identification card (ID) before allowing a vehicle to enter a military installation.
Drop Arm Optical Turnstiles Manufactured by Q-Lane Turnstiles LLc
Underground entrance to the New York City Subway system
Physical security access control with a hand geometry scanner
Example of fob based access control using an ACT reader
Various control system components
Typical access control door wiring
Access control door wiring when using intelligent readers
Access control system using serial controllers
Access control system using serial main and sub-controllers
Access control system using serial main controller and intelligent readers
Access control systems using serial controllers and terminal servers
Access control system using network-enabled main controllers
Access control system using IP controllers
Access control system using IP readers
Access control door wiring when using intelligent readers and IO module

1) A service feature or technique used to permit or deny use of the components of a communication system.

Communication system

Called-party camp-on

Communication system

In telecommunication, a called-party camp-on is a communication system service feature that enables the system to complete an access attempt in spite of issuance of a user blocking signal.

The asteriskos used in an early Greek papyrus.

Essential service (telecommunications)

The asteriskos used in an early Greek papyrus.

In telecommunication, an essential service (critical service) is a network-provided service feature in which a priority dial tone is furnished.

The asteriskos used in an early Greek papyrus.

Automatic redial

The asteriskos used in an early Greek papyrus.

In telecommunication, an automatic redial is a service feature that allows the user to dial, by depressing a single key or a few keys, the most recent telephone number dialed at that instrument.