Common Area Phones

Actually some devices labeled as 'Common Area Phones' like the Polycom CX500 are NOT supported witrh Skype for Business Online.  These devices do not include a USB port and thus cannot be authenticated.  SfB Online does not support PIN Authentication which is the only way to the traditional Common Area Phone account can authenticate.

This article covers user account/license requirements for phones used online: http://blog.schertz.name/2017/01/skype-for-business-online-meeting-room-accounts/

Using other 3PIP devices can emulate this approach buy using a regular user or meeting room account online (not CAP accounts).