If you use Slack in the workplace you are likely familiar with the benefits and how much of a use it can be for communicating with team members. There are loads of useful features like channels and more personal direct messages, but a little over a month ago Slack also introduced a new way to communicate between team members via the "Calls" feature. At the time it was in beta testing and it continued to stay that way for the next month, but as of a couple of days ago Slack has officially removed the Call feature from beta and has made it available to all Slack users.
Slack is rolling out calling across the entire service, so it'll be available via Windows and Mac apps, as well as in Google Chrome, and in the Android and iOS apps, although it appears that the update may be staggered and rolling out to people in stages, or it could just be a server side thing that Slack has to turn on for users on their end. In the Windows, Mac, or Chrome versions of Slack, there will be a new phone button that you should see placed right next to the settings "gear" icon at the top of the app panel.
Inside of the Android app if you're prone to using Slack on mobile and on the go, call functionality will be an option that you see inside of the dropdown menu in channels and in DMs. One-on-One calls are available to any Slack user, paid or not, but if you are a paid team then you'll have the ability to do group calls from inside of any channel or group direct message as well. Over the next couple of days, users should start to see the Slack calling feature appear in all the forms that they interact with the tool. It's also worth noting that calls only support voice at the moment, although it has been announced that native video calling is coming to Slack at some point in near future as this was initially unveiled by Slack back in March.