What number is commonly used nationwide for directory assistance by carriers?

The number commonly used nationwide for directory assistance by carriers is 411. This number provides a service that allows individuals to obtain telephone listings and information about businesses and residences. When a caller dials 411, they are typically connected to a service representative who can assist with locating a specific number or providing additional information.

In contrast, 911 is designated for emergency services, allowing individuals to reach police, fire, and medical assistance in urgent situations. The number 511 is used for traffic and travel information, helping drivers with real-time updates on road conditions, traffic advisories, and public transportation schedules. The number 4111 does not exist as a widely recognized directory assistance number, making it an incorrect choice in this context.

Using 411 simplifies the process of finding contact information and is well understood across the United States as the go-to directory assistance number, making it the correct response in this question.