A vertical service code (VSC) is a sequence of digits and the signals star (*) and pound/hash (#) dialed on a telephone keypad or rotary dial to access certain telephone service features.
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 instead of out (horizontally) to another telephone company.
The following are the vertical service codes generally recommended by the North American Numbering Plan Administrator for use in the NANP territories.
Local Area Signalling Services (LASS) and Custom Calling Feature Control Codes:[1][2][3] This article incorporates public domain material from Federal Standard 1037C.