Here is a feature many of my customers have asked for ever since switching from Skype for Business Online to Teams: Teams/Skype Consumer chat and calling interop.
The feature is listed as Roadmap ID: 53935
According to the message center, the feature will be rolling out in a disabled state, and admins will have to log into the Teams Admin Center to configure it under "external access":
Once configured, users can search the external directory, the same way they can search for internal chat users:
Once set up, users can chat, call by audio or video, just as they can with other Skype for Business or Teams users. There are a couple of limitations in this initial release, such as no rich formatting, no mentions or emojis. It also looks like you can't search for a Skype ID or phone number, but it is all documented in the interop description found at docks.
And just like that, the world became a little smaller.....