chat between MS Teams und Skype for Busines

Complicated story, but yes you can do chat and calls! The experience is rather limited regarding chat ( plain text chat only ) screen sharing compability is coming though also!
How this works also depends on coexistence mode! Read more here:

https://docs.microsoft.com/en-us/microsoftteams/teams-and-skypeforbusiness-coexistence-and-interoperability