A group of users can be created with a purpose of receiving voice announcements through the speaker of a telephone set, but it has to be in the waiting mode.
The system of Classes of Service (COS) helps defining rights for one or another extension in the PBX or Centrex systems. For example, few groups require more space for storing voice messages, while other need the redirection of calls to cell phones, the third does not have to make calls outside of the office network. With the help of this system one can change and configure settings.