"Anyone can make one-on-one calls, while paid teams can also make group calls in any channel or group DM. When someone initiates a call, a message will appear, inviting you to join the call.Calls come to Slack — Several People Are Typing — The Official Slack Blog
Best of all, calling your teammates in Slack saves everyone the fuss of digging through calendar invites for call numbers and dial-in codes and all the rest. That’s a bit of worky-work we can probably all let go.
Calls even have an emoji response feature. Clicking one of the pre-selected emoji will display it over your avatar for a moment along with a subtle sound, allowing you to express approval, disapproval, or raise your hand to ask a question — all without interrupting the speaker."
Wednesday, June 08, 2016
Calls come to Slack — Several People Are Typing — The Official Slack Blog
Audio + emoji