Likely need the phone operations team to manually put it on your line - tech support to submit a ticket.
However, turning it on and off as you desire will not be an option.
If I recall correctly, *99 used to work to set it up, but I believe that *99 as been disabled on all lines now.
This is not likely a good idea if you are using a cell phone for example. Turning off your cell phone would have all calls go go your cell's voice mail (because it would answer first).
Yes, I am not employed and looking for IT work. Have passport, will travel.