From Zenitel Wiki
When lifting the handset of a station, a call can automaticaly be placed to a preconfigured number. This is known as Hotline Call. By default there is a delay of 5 seconds before the call is made, allowing the user to dial a different number on the keypad. This delay can be set to a low value if immediate call is required.
Enable the hotline function by selecting the hotline station in the listbox in Users & Stations, select the Station Type tab, and check the Hotline flag:
In Users & Stations, select the DAK button, and enter the call destination on DAK 7:
Option: If the hotline call should generate a Call Request instead, enter "I 623 I xxx" on DAK 7, where xxx is the target station. If the Call Request should be cleared when replacing the handset, enter "I626 I xxx" on DAK 8, else leave DAK 8 blank.
Hotline Call Delay
By default there is a 5.0 second delay from the handset is lifted until the call is placed. Often you want the call to be placed immediately. To change the delay time, select Exchange & System, System, Calls and Options. Hotline Call Delay.