A vertical service code (VSC) is a special code dialed prior to (or instead of) a telephone number that engages some type of special telephone service or feature. Typically preceded with an asterisk, or * (star), key on the touch tone keypad and colloquially referred to as star codes, most are two digits in length; as more services are developed, those that use 2 or 3 as the first digit are sometimes three digits in length.