Yes! Session currently has an open beta program available to all users where you can test the early versions of this feature.
To enable calls, follow these steps:
Mobile (iOS and Android)
1. Open Settings
2. Tap on "Privacy"
3. Toggle on "Voice and Video Calls"
Desktop
1. Open Settings
2. Navigate to "Permissions"
3. Toggle on "Voice and Video Calls (Beta)"
If you want to learn more about calls, check out this video: