Only Intermedia Unite enabled users can use Voice services and be a part of the Hunt Group or Contact Center Express. 

Users can be added to the Contact Center as Agents or Managers.

Agents will receive calls forwarded to the Contact Center group.
Managers are able to see active calls, agents' statuses, and have the ability to monitor/whisper/barge agent's calls. Special Contact Center Express tab is available for them in the Intermedia Unite Desktop Application.

To become agents or managers, users should have Contact Center functionality enabled in HostPilot.
This can be checked or enabled/disabled in Intermedia Unite > Contact Center > Users.
You will see the list of users with Contact Center functionality enabled.

If you want to enable Contact Center for the user please click on Users without Contact Center link and check the box for the user. Then click Proceed.

If you want to disable Contact Center for the user please click on Users with Contact Center link and uncheck the box for the user. Then click Proceed.

More information about Contact Center management can be found in the article Managing Contact Center Express .