Reserved Extensions

Updated at April 25th, 2025

Table of Contents

Differing Digits Reserved Extension List Emergency Avoid List

Differing Digits

Systems may have different digits, so the reserved extensions listed below are shown in the following format:

2-digit/3-digit/4-digit/5-digit - Purpose

For example 10/100/1000/10000. Extension 100, 1000, or 10000 are not reserved on a 2-digit system, however you cannot use them as extension values.

10|100|1000|10000 - Reserved only until you replace the Operator Extension, then you can delete this extension.
70|700|7000|70000 - Reserved for the Conference Calls feature. This can be changed to any other unreserved value using the article Updating Conferencing Settings.
77|777|7777|77777 - Permanently Reserved for the PIN Protect IVR. This cannot be modified.
88|888|8888|88888 - Reserved for the built-in Phone System Fax server. This can only be changed with the help of Support.
98|998|9998|99998 - Permanently Reserved for bvoip system management purposes. This cannot be modified.
99|999|9999|99999 - Reserved for the Voicemail system. See Managing Voicemail Setup and Settings for how to change this, if for example you need to use 999 as your emergency number.

We recommend you avoid using the following extensions which are used as emergency numbers, if you plan to work in any of these regions: