The following numbers should not be assigned within a domain because they are reserved for system functions.


Restricted Numbering
00-99Reserved for internal use

611

Customer Service

911

Emergency

933Emergency Testing
988National Suicide Hotline

700-799

Used for Dynamic Call Parking Queues

900-999

Reserved due to 911 system feature

5000/9900

Unregistered Login to VMail (prompted for acct no and password)

5001/9901

Registered Login to VMail (prompted for password only)

5002/9902

Hot Desking Sign In

7000-7999These are unusable as extension numbers because they conflict with the 7+extension rule to transfer a call directly to voicemail
9900-9999System Features
Best Practice Dial Plan

100-599

User Extensions

800-899User Extensions
1000-4999User Extensions
5003-6999User Extensions
8000-8999User Extensions
9000-9899Special Extensions (Example : Cloud Extension that forward to a cell phone, Fax Users, call routing, call queues and auto attendants)