MS TEAMS: Set your coexistence and upgrade settings

 https://learn.microsoft.com/en-us/microsoftteams/setting-your-coexistence-and-upgrade-settings

In the Microsoft Teams admin center, in the left navigation, go to Teams > Teams upgrade settings.

At the top of the Teams upgrade page, modify the following options as desired.

• Set the Coexistence mode.

  • Islands - Use this setting if you want users to be able to use both Skype for Business and Teams simultaneously.

  • Skype for Business only - Use this setting if you want your users to only use Skype for Business.

  • Skype for Business with Teams collaboration - Use this setting if you want your users to use Skype for Business in addition to using Teams for group collaboration (channels).

  • Skype for Business with Teams collaboration and meetings - Use this setting if you want your users to use Skype for Business in addition to using Teams for group collaboration (channels) and Teams meetings.

  • Teams only - Use this setting if you want your users to use only Teams. Note that even with this setting, users can still join meetings hosted in Skype for Business.