Editing Vertical service code (section)

{{Short description|Telephone dialing code for access to service features}}
{{use American English|date=September 2022}}
{{use MDY dates|date=September 2022}}

A '''vertical service code''' ('''VSC''') is a sequence of digits and the signals [[Asterisk|star]] ({{Key press|*}}) and [[Number sign|pound/hash]] ({{Key press|#}}) dialed on a [[telephone keypad]] or [[rotary dial]] to access certain telephone service features.<ref name="NANPA">{{Cite web |title=Vertical Service Codes – Code Definitions |url=https://nationalnanpa.com/number_resource_info/vsc_definitions.html |publisher=North American Numbering Plan Administrator |website=NationalNANPA.com |access-date=2022-07-30 }}</ref> Some vertical service codes require dialing of a [[telephone number]] after the code sequence. On a [[touch tone]] telephone, the codes are usually initiated with the [[Asterisk#Telephony|star key]], resulting in the commonly used name ''star codes''. On rotary dial telephones, the star is replaced by dialing ''11''.

In [[North American]] [[telephony]], VSCs were developed by the [[American Telephone and Telegraph Company]] (AT&T) as '''Custom Local Area Signaling Services''' ('''CLASS''' or '''LASS''') codes in the 1960s and 70s. Their use became ubiquitous throughout the 1990s and eventually became a recognized standard. 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 [[telephone exchange|central office]] instead of out (''horizontally'') to another telephone company.