Include in open duplex conference feature
From Zenitel Wiki
| Feature: | Duplex Conference - Include |
| Default directory number: | 56 - during conversation |
| Feature number: | 89 |
| Parameter 1: | 0 (N/A) |
| Description: | A participant in a duplex conference can include other stations into the conference.
Dial 56 + directory number (station or group) The dialler immediately goes back to the conference after terminating the dialling. |