N11 code

For example, 411 and 611 are commonly used in the United States, but not officially assigned by the Federal Communications Commission.

The designation for special use in the NANP prevents their use as area codes and central office prefixes, eliminating about 8 million telephone numbers from assignment.

411 and 611 (formerly 811) are typically blocked within enterprise or private branch exchange (PBX) systems, including cellular telephone service purchased for an enterprise system, since 411 calls generally incur a fee and the service is now readily accessible by other means, and 611 services are managed by the enterprise in which the phone resides.

Likewise, local, state or provincial government may, but do not uniformly, operate traffic information using 511.

Within the NANP, a leading digit of 0 or 1 indicates special dialing arrangements.