This solution occupies in-between position between solutions PBX and Virtual PBX.
Principally, you just add Billing to PBX solution, but don't give your users rights to add or remove users as in solution Virtual PBX.
Work on adding, deleting users, internal short extensions and SIP accounts is performed by your company's employees.
Configuring this solution is described in section Configuring virtual PBX without administrator access