How can customers use Teams and Skype for Business side by side?
Since there is some overlapping functionality between Teams and Skype for Business, it is important to begin with a user pilot. A pilot is a small-scale deployment that enables a customer to validate the interoperability with Skype for Business in their environment as well as understand how their end-users can maximize their productivity while minimizing confusion with both products running side-by-side.
For steps on resources and tips, go here: https://docs.microsoft.com/en-us/MicrosoftTeams/pilot-essentials