Extension Numbering & Reserved Number Space
Written by Marissa Orsini
Updated at August 17th, 2023
Table of Contents
Scope
Intended Audience: All Users
This article outlines the reserved and permitted numbering schemes to use for extensions and features.
Restricted Numbering
This table outlines numbering schemes that may only be used for their designated purpose. Extensions created outside of the specified purpose will not work.
| Extension Range | Designated Purpose |
|---|---|
| 0 - 99 | Reserved for internal use |
| 211 | FCC standard for community support information (free and confidential services) in some regions of the United States |
| 311 | FCC standard for municipal government services (non-emergency line) in some regions of the United States |
| 411 | Local Directory Assistance |
| 511 | FCC standard to access traveler information services in some regions of Canada and the United States |
| 611 | Customer Service |
| 711 | FCC requirement to connect a deaf caller to a Telephone Relay Service |
| 811 | Call Before You Dig |
| 911 | Emergency Services |
| 933 | Emergency Testing |
| 988 | National Suicide Hotline |
| 700 - 719 | Call Parking without Ringback |
| 720 - 799 | Call Parking with Ringback |
| 5000 | Unregistered Login to Voicemail - Prompts for extension and password |
| 5001 | Registered Login to Voicemail - Prompts for password only |
| 9900 | Unregistered Login to Voicemail - Prompts for extension and password |
| 9901 | Registered Login to Voicemail - Prompts for password only |
| 9902 | Hot Desking Sign In |
| 7000 - 7999 | Transfer to Voicemail |
| 9900 - 9999 | Reserved for System Features |
Recommended Numbering
This table shows the recommended numbering scheme for extensions. The numbering scheme here is for reference and normalization purposes only, and does not need to be followed.
| Extension Range | Recommended Purpose |
|---|---|
| 100 - 599 | User Extensions |
| 800 - 899 | User Extensions |
| 1000 - 4999 | User Extensions |
| 5003 - 6999 | User Extensions |
| 8000 - 8999 | User Extensions |
| 9000 - 9099 | Auto Attendants |
| 9100 - 9199 | Call Queues (Excluding Call Parks) |
| 9200 - 9299 | Special Extensions such as Forwarding Users, Call Routing Users, Analog/Paging Systems, & Fax Users |