For a short period (up to an hour) during the service set-up, spare licences are required. A recommendation if there are not free licences on the customer tenant is to use one of several free trial offers available from Microsoft to Office 365 Customers. Microsoft Free Trial offers do not automatically convert to paid services.

In this example we will select the Common Area Phone free trial as this offer provides the required licence for the set-up and  the free trial can be added to up to 25 users to provide the calling capability required for the service (there's no limit to the number of licences that can be purchased).

1. Go to the Admin console for Office 365 and select the Billing tab on the left, then select “Purchase Services”

2.  On the right-hand pane a selection of Office 365 services can be seen to review

3. In the  Search box enter "Common Area"

Here you will see the Common Area Phone offer.

4: Select the offer

Note: the free-trial option may not show if the free trial has previously been used.

4. Select the “Get free trial” button

5. Microsoft may ask for identity verification by text message

6. A final confirmation is offered to start the trial and the licences will be available on the account