Which number is used by local exchange carriers for business office use?

The number designated for business office use by local exchange carriers is 811. This number is primarily associated with "Call Before You Dig" services, which is crucial for ensuring safety and preventing accidents related to underground utilities. When someone calls 811, they are connected to the appropriate utility companies to identify and mark the locations of underground lines before any excavation or digging takes place.

In this context, 811 serves as an important tool for both public safety and infrastructure protection, making it a preferred choice for local exchange carriers in relation to business office use. The other numbers provided serve specific purposes: 911 is for emergency services, 800 is typically associated with toll-free calling, and 311 is a non-emergency municipal service line. Each of these has distinct functions and is not utilized in the context of local exchange carrier business offices in the same manner as 811.