Vertical service code

A vertical service code or VSC is a special code dialed prior to (or instead of) a telephone number that engages some type of special telephone service. 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 although, 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 as Custom Local Area Signaling Services or CLASS codes (or LASS) in the 1960s and 70's. Their use became ubiquitous throughout the 1990s and eventually became a recognized standard. As CLASS was an AT&T trademark, the moniker of Vertical service codes was adopted by the North American Numbering Plan Administration. The use of the word "vertical" is a somewhat arcane tip of the hat 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 to another telephone company.

Other dialing formats

In most cases VSCs can also be accessed from rotary phones by dialing 11 instead of the * prior to the code (1167 instead of *67 will typically work on any North American telephone to enable Caller ID privacy), or on some carriers, by dialing the code alone (activating after a pause). Because of historical usage by some telephone switch manufacturers, in some areas VSCs may also be dialed by placing a # (hash or pound key) after the code, instead of a * before it (72# instead of *72 for Call Forwarding).

GSM cellular telephone carriers provide codes similar to VSCs using a # as the leading character. Because these pound codes are not part of the NANPA system, they are not considered Vertical Service Codes. However, many NANPA VSCs have also been adopted by cellular carriers (e.g., 72 for forwarding, 67 for Caller ID blocking), and some VSCs were created specifically for mobile carriers (such as 228 and 272). cdmaOne carriers in North America use only VSCs.

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.

Local Area Signalling Services (LASS) and Custom Calling Feature Control Codes:

Sortable table

Service	Tone	Pulse/rotary	Notes
Cancel forwarding	30	n/a	[C1]
Automatic Forwarding	31	n/a	[C1]
Notify	32	n/a	[C1] [2]
Intercom Ring 1 (short short)	51	1151	[3]
Intercom Ring 2 (short short long)	52	1152	[3]
Intercom Ring 3 (short long short)	53	1153	[3]
Extension Hold	54	1154	[3]
Customer Originated Trace	57	1157
Selective Call Rejection (or Call Screen)	60	1160
Selective Distinct Alert	61	1161
Selective Call Acceptance	62	1162
Selective Call Forwarding	63	1163
ICLID Activation	65	1165
Busy Number Redial	66	1166
Number Display Blocking	67	1167	[4]
Computer Access Restriction	68	1168
Call Return (incoming)	69	1169
Call Waiting disable	70	1170	[4]
No Answer Call Transfer	71	1171
Usage Sensitive 3 way call	71	1171
Call Forwarding: start	72	1172
Call Forwarding: cancel	73	1173
Speed Calling (8 numbers)	74	1174
Speed Calling (30 numbers)	75	1175
Anonymous Call Rejection	77	1177	[5] [M: *58]
Call Screen Disable	80	1180	(or Call Screen) [M: *50]
Selective Distinct Disable	81	1181	[M: *51]
Number Display Unblocking	82	1182	[4] [7]
Select. Forwarding Disable	83	1183	[M: *53]
Caller ID Disable	85	1185
Busy Number Redial Cancel	86	1186	[6] [M: *56]
Anonymous Call Rejection Disable	87	1187	[5] [M: *68]
Call Return Cancel	89	1189	[6] [M: *59]

Notes

[C1] - Means code used for Cellular One service
[1] - for cellular in Pittsburgh, PA A/C 412 in some areas
[2] - indicates that you are not local and maybe how to reach you
[3] - 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
[4] - applied once before each call, you can not block caller ID to 800 numbers
[5] - A.C.R. blocks calls from those who blocked Caller ID (used in C&P territory, for instance)
[6] - cancels further return attempts
[7] - *82 (1182) has been mandated to be the nationwide code for "Send CLID info regardless of the default setting on this phone line."
[M: *xx] - alternate code used for MLVP (multi-line variety package) by Telcordia Technologies, (formerly Bellcore). It goes by different names in different RBOCs. In Bellsouth it is called Prestige. It is an arrangement of ESSEX like features for single or small multiple line groups. The reason for different codes for some features in MLVP is that call-pickup is *8 in MLVP so all *8x codes are reassigned *5x

• Custom Local Area Signaling Services (CLASS) are PSTN telephony intelligent network services beyond basic voice calling, such as caller ID (automatic number identification (ANI)), caller number blocking, automated call return, call blocking or screening. Different IXCs offer various services. Late in the 20th century the term was simplified to LASS.

• The services rely on the ITU-T standard Signalling System 7 (SS7) connectivity between network switches (SSPs) and databases (800 Database, LNPDB, LIDB, etc.) to operate. The CLASS standards were defined by Bellcore (now Telcordia Technologies) in the 1970s.

• Some services such as call forwarding, three-way calling, call waiting, or speed dialing were sometimes considered part of custom calling rather than CLASS/LASS.

See also

• Prompt voice for most U.S. AT&T implementations of VSC features is Pat Fleet
• Mobile dial code

References

• Vertical Service Codes - North American Numbering Plan Administration (NANPA)
•  This article incorporates public domain material from the General Services Administration document "Federal Standard 1037C".