What are some features of a PBX?

I can explain the PBX common features on Zadarma PBX example. Zadarma PBX offers: 1. Call recording and call transfer with call performance statistics. 2. PBX integration with CRM systems, including Zadarma’s Teamsale CRM.3. Push notifications for messaging. 4. Speech recognition and speech analytics. 5. Multiple lines and phone numbers. 6. Incoming call scenario settings, and voice menu. 7. Voice mail and automated responses. 8. Caller IDs. 9. Visual PBX editor. 10. Automatic call forwarding. 11. Video conferencing. 12. Call holding and queuing. Also, Zadarma’s PBX offers call barging and whispering modes features as well as call analytics.