Aastra Telecom 6753I - Manual (Page 107)

Model 6753i IP Phone User Guide 99
Line Keys and Programmable Keys
1. Click on Operation->Programmable Keys.
or
Click on Operation->Expansion Module <N>.
Programmable Keys and Expansion Module Keys
2. Select from "Key 3" through "Key 6".
or
Select from “Key 1” through “Key 36” (M670i).
3. In the "Type" field, select Conference.
4. Click to save your changes.