With more organizations adopting Microsoft teams and upgrading from Skype for Business, there are more users in those organizations that have a mix of Microsoft Teams and Skype for Business usage.
The experience of one user using Microsoft Teams, and another user using Skype for Business largely depends on what coexistence mode each user is in. The coexistence mode is set in a Teams Upgrade policy which applies to the user account. There is a global Teams Upgrade policy defined at the tenant level which takes precedent if there is no Teams Upgrade policy applied to the user.
I often get questions from a Skype for Business user when . . . → Read More: Teams and Skype Interop Feature Limitations & Workarounds