...

A fourth option is to use the SOAP interfacs provided by sipXconfig

Manage Users in Groups

Users can and should be members of one or several groups. Groups not only allow you to logically group users together, but groups are also used to define permissions. Therefore, before you start creating all your users, think about what permissions you want to assign to these users and group them accordingly.

...

Alternatively, User IDs can reflect extension numbers, Direct Inward Dialing numbers, or some other numbering scheme that you administer.

...