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.
This does not work. I cant message someone using SfB as it finds their Teams client even if they are not signed in. They get message saying your teammates are trying to reach you in MS Teams.
But if they start the conversation using SfB, its fine.
Thanks to those of you who participated in the session with our user research team. We are continuing to work on this important feature, and will update you as we get closer to completing. ~ Alex