Microsoft Teams, the hub for teamwork in Office 365, continues to bring new capabilities to empower teams and organizations to achieve more. With new features like Quiet Hours, users can enjoy enhanc...
Updated Aug 25, 2022
Version 7.0
Blog Post
If MS has upgraded to you "Teams Only" mode, you can still put in an Office 365 support ticket and ask to be sent to back-end team to re-enable Skype for Business Islands mode. Give them permission to change your tenant settings on the back-end. Once sent to the back-end team, it takes about 24 hours to be applied. This will let you switch between the different co-existence modes again in the Teams admin interface (and presumably via Powershell)
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I've done this more than once, with more than one of my tenants. I give the reason that Teams does not (yet) support Skype (Consumer) federation and I get no questions. As long as S4B is officially supported until July 2021, I'm going to keep using it. The Teams chat/IM/video interface is just too bloated compared to the streamlined S4B client when all you want to do is IM/video message and have an organized list of contacts and favorites.
As a side note, if you would like to see a streamlined IM-centric "version" of the Teams client that more closely resembles the Skype for Business client, you can vote for it at the Teams UserVoice site here.