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As CLASS was an AT&T trademark, the term vertical service code was adopted by the North American Numbering Plan Administration. The use of vertical is a somewhat dated reference to older switching methods and the fact that these services can only be accessed by a telephone subscriber, going up ( vertically ) inside the local central office ...
Call forwarding is often enabled by dialing *72 followed by the telephone number to which calls should be forwarded. Once someone answers, call forwarding is in effect. If no one answers or the line is busy, the dialing sequence must be repeated to effect call forwarding. Call forwarding is disabled by dialing *73.
10-10-321, 10-10-345, 10-10-220, and 10-10-987 are United States long-distance phone services best known for their prolific television and direct mail advertising in the late 1990s. 10-10-321 was the first mass-marketed service of its type. 10-10-345 was owned by AT&T, and the rest were all owned by MCI, which is now part of Verizon.
An off-premises extension (OPX), sometimes also known as off-premises station (OPS), is an extension telephone at a location distant from its servicing exchange.. One type of off-premises extension, connected to a private branch exchange (PBX), is generally used to provide employees with access to a company telephone system while they are out of the office.
Extensions that were busy or rang "no answer" would forward to the message center using a device called a "call director". The call director had a button for each extension in the company which would flash when that person's extension forwarded to the message center. A little label next to the button told the operator the person being called.
The test consists of calling a reverting calling telephone number (ringback number) or a vertical service code with a standard telephone. Upon answering the call, the exchange plays a unique signal tone as a signal for the installer to hangup the telephone. The exchange then places a reverting call to the originating line, causing the telephone ...
In the United States, both interexchange carriers (IXCs) such as Sprint, AT&T Inc., and Verizon, and Local Exchange Carriers (LECs) such as Verizon and AT&T offer toll-free services. [2] [3] The way that a toll-free number is handled depends on whether it is a domestic or an interexchange call.
In this case, AT&T Illinois bills the call. (area code) 555–1212: National Directory Assistance. This example assumes the caller is in Oak Brook, Illinois (area code 630) and uses Verizon as their long-distance carrier. Example: The caller is looking for a listing in Los Angeles, California (area code 213) and dials 213-555-1212.