Yes, you can - but you need to change the time on the system as the telephone gets the time from that. What type of Comdial system do you have? It may say on your manual, but more than likely you will need to describe it if you already do not know.

It could look like the following:
1)a reasonably flat grey metal rectangular box,
2)a large black squarish box that says "DXP" or similar
3)a grey tower (like a large PC) that says FXT or FXS
4)a square grey or black box that says FXII.

Likely it will be located in a closet or room somewhere in your office or building.

Steve