The 8024S-GT is the model number for a black LCD speaker phone and not the system. Messages are not left on the main line but you can use the operator mail box which is what I think you mean anyway. Where is your phone vendor, they should be able to set this up and show you how to change messages. It depends on what voicemail box owns the routing box which is your main gretting. By default it is mail box 70. Do you have access to that mainbox?