Vertical service code
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.
In North American telephony, VSCs were developed by AT&T Corp. as Custom Local Area Signaling Services or CLASS codes (sometimes LASS) 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 the word "vertical" is a somewhat dated reference to older switching methods and the fact that these services can only be accessed by a local telephone subscriber, going up (or vertically) inside the local central office instead of out (or horizontally) to another telephone company.
List of vertical service codes
The following are the VSCs generally used in the North American Numbering Plan. Not all of these services are available in all areas, and some are only available to landline or cellular telephones. Some require additional services be purchased from the telephone company to use them.
|Cancel forwarding[note 1]||*30||N/A|
|Automatic forwarding[note 1]||*31||N/A|
|Intercom ring 1 (short short)[note 2]||*51||1151|
|Intercom ring 2 (short short long)[note 2]||*52||1152|
|Intercom ring 3 (short long short)[note 2]||*53||1153|
|Extension hold[note 2]||*54||1154|
|Malicious caller identification||*57||1157|
|Selective call acceptance||*62||1162|
|Selective call forwarding||*63||1163|
|Number display blocking (per call)[note 3]||*67||1167|
|Activate call forwarding on busy||*68||1168|
|Last-call return (incoming)||*69||1169|
|Call waiting disable[note 3]||*70||1170|
|Conditional forward: No answer[note 4]||*71||1171|
|Usage sensitive three-way call||*71||1171|
|Unconditional forward: All calls||*72||1172|
|Call forward: Cancel||*73||1173|
|Speed calling (8 numbers)||*74||1174|
|Speed calling (30 numbers)||*75||1175|
|Anonymous call rejection[note 5]||*77||1177|
|Do not disturb||*78||1178|
|Do not disturb disable||*79||1179|
|Call blocking disable||*80||1180|
|Priority call disable||*81||1181|
|Caller ID (per call)[note 3][note 6]||*82||1182|
|Selective call forwarding disable||*83||1183|
|Caller ID disable||*85||1185|
|Continuous redial cancel[note 7]||*86||1186|
|Anonymous call rejection disable[note 5]||*87||1187|
|Deactivate call forwarding on busy||*88||1188|
|Last-call return cancel[note 7]||*89||1189|
|Conditional forward: Busy line||*90||1190|
|Conditional forward: No answer||*92||1192|
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- Code used for Cellular One service
- Found in Pac Bell territory. Intercom ring causes a distinctive ring to be generated on the current line. Hold keeps a call connected until another extension is picked up.
- Applied once before each call. Caller ID to 8xx NPA numbers and 911 cannot be blocked.
- Used by certain carriers (like Verizon Wireless), but this use is non-standard.
- ACR blocks calls from those who blocked Caller ID (used in C&P territory, for instance)
- Has been mandated to be the nationwide code for, "Send CLID info regardless of the default setting on this phone line."
- Cancels further return attempts
- Mobile dial code
- Pat Fleet – Prompt voice for most U.S. AT&T implementations of VSC features
- Public switched telephone network
- Signalling System 7