Contoso needs to configure the user accounts of the sales department users. To meet the company's compliance policy, users in the sales department must continue to use on-premises Skype for Business…

The "Skype for Business with Teams collaboration and meetings" coexistence mode allows users to continue using on-premises Skype for Business for chat, calling, and presence, while enabling Teams for channel-based collaboration and meetings. This precisely meets the requirement for on-premises Skype for Business for IM/calling and allowing other Teams functionalities.

While Grant-CsTeamsUpgradePolicy is the correct cmdlet for PowerShell, the specific policy name "SfBWithTeamsCollab" (Skype for Business with Teams collaboration and meetings) is typically applied as a mode, and the question asks for a step from the admin center, making A more direct for that context, assuming it's an option there.

The "Islands" mode allows users to run Skype for Business and Teams in parallel, with each client providing full functionality, which doesn't restrict Skype for Business to IM/calling only.

"Skype for Business coexistence mode" is a generic term; the specific "Skype for Business with Teams collaboration and meetings" mode is required to allow only IM and calling on SfB while still using Teams for collaboration and meetings.