It looks like some people in the thread below have figured it out — we actually have this. You can start a chat both ways; the system will automatically recognize if this person is on Skype for Business or on Teams.
Thanks and let me know if you have any questions.
An error occurred while saving the commentAnonymous commented
I have followed what Jan has recommended, however the Chat box in Teams got disappeared.
I even tried to enable SfBWithTeamsColl organization wide, and all the users Chat box got disabled as well. So I am not pretty sure that would be it.
Can someone advise on this.