What is a fixed dialing number?

A fixed dialing number (FDN) is a feature found in many mobile phones that allows users to create a list of phone numbers that are allowed to be dialed from that phone. This control function is especially useful in situations where users want to restrict outgoing calls to a limited set of approved or emergency numbers.

Here are some key points about fixed dialing numbers:

1. Purpose: FDN allows the device owner to limit outgoing calls to specific numbers, ensuring control over who can be contacted. This feature is particularly important for businesses, parents, or individuals who want to restrict phone usage to a specific set of contacts.

2. Authorized numbers: With FDN, users can create a list of phone numbers that are allowed or trusted, typically stored in a separate access-controlled section of the phone's memory. Only these pre-authorized numbers can be dialed while FDN is enabled.

3. Call barring: FDN works in conjunction with call barring, which is a feature that restricts outgoing calls or certain types of communication services. While call barring controls the types of calls that can be made (international calls, premium numbers, etc.), FDN specifies the exact phone numbers that are permitted.

4. Emergency numbers: Even when FDN is activated, emergency numbers like 911 or other local emergency services are usually exempted and can be dialed. This ensures that necessary emergency calls can still be made regardless of any restrictions in place.

5. Configuration: The FDN feature can usually be configured through the phone's settings or security options. Users can add or delete numbers from the authorized list as required, and some devices also offer PIN protection to restrict changes to the FDN settings.

6. Use cases: Fixed dialing numbers are commonly utilized in business environments, where companies issue phones to employees but want to control outgoing calls to only important contacts. Additionally, parents may employ FDN on their child's phone to restrict calling capabilities to select family members or trusted contacts.

It's important to note that the availability and functionality of FDN may vary depending on the mobile phone model and operating system.