Carrier Identification Code
Each carrier (interexchange or local exchange) is assigned a four-digit identification code, the Carrier Identification Code (CIC) which was used with feature groups. The interexchange carrier to which calls from a subscriber line are routed by default is known as the Presubscribed Interexchange Carrier (PIC). To give telephone users the possibility of opting for a different carrier on a call-by-call basis, Carrier Access Codes (CAC) were devised. These consist of the digits 101 followed by the four-digit CIC. The CAC is dialled as a prefix immediately before dialing a long-distance phone number.
In popular usage, CACs are often referred to as dial-around codes (because they allow dialing around the PIC). Sometimes they are even called "PIC codes", though this term is inaccurate, since the code is being used to avoid the PIC, not to use its services.
When CICs were first introduced in 1983, they were only three digits long, and the CAC consisted of the digits 10 followed by the three-digit CIC. In 1998, the CIC had to be extended to four digits. Existing carriers' codes were prefixed with zero. Thus, a pre-1998 CAC of the form 10-XXX became 101-0XXX. Since the CACs starting with 10-10 are generally the oldest and best-known ones, CACs are sometimes referred to as 10-10 codes.
Use of CACs is popular with telephone users who wish to avoid paying a regular monthly fee for access to inexpensive long-distance service. They can also be useful if encountering a "circuits busy" condition when all long distance trunks are tied up; a CAC allows selection of an alternate carrier, which may have other open long-distance trunks. This feature gave rise to slamming and the lesser known cramming technique of telephone fraud.
As multiple competitive long-distance carriers have been permitted in countries other than the United States, schemes similar to the CIC/CAC have spread worldwide. They are now used in (among other countries) Canada, Germany, and Japan.
Although CAC are no longer widely used, PIC and CIC are still common.
Read more about this topic: Interexchange Carrier
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