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: | During Duplex Conference: Include one new member.
Dial: <dir.n> <user dir.no>. Dialing station returns to the conference, while the included station starts to ring. |