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.
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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.
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:
| 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] |
[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