Keep in mind: Calls (beta) is currently voice only and desktop only. Video, screen sharing, and mobile support will come in the future.
包括了 one-to-one (開放給所有的 plan)，以及 group (開放給付費 plan)。
在 troubleshooting 的說明裡有提到技術問題，也可以看出一些東西：
If Slack is having trouble establishing a call connection, check the following settings, or ask your IT admin to do so:
- Set your network to allow outbound UDP connections to port 22466.
- Make sure your network is allowing incoming traffic from UDP 22466.