The system can use a mix of extension numbers up to 15 digits in length. By default, hunt groups and extensions are given 3-digit extension numbers starting from 200 upwards.
To renumber all user extensions using IP Office Manager:
IP Office Manager can be used to renumber all extensions on the system. This will also update any references to the extension number in other configuration fields.
1.With the system configuration, select Tools | Extension Renumber.
2.Select the range of existing user extensions you want renumber and enter the new starting extension number for that range.
3.Click OK.
4.Either:
•Continue the basic configuration using the following sections of this chapter and then save the configuration when finished.
•Save the configuration as it currently is. This may cause the system to reboot, the save menu will indicate if that is required. After saving the configuration, reload the configuration and continue with configuration.
5.Continue with the basic configuration or click on the 
save icon to save the updated configuration and then continue.