I would like to add the printer, ip phone, network switch, etc as a inventory to manage. I know I can't manage those devices actually, the purpose to doing this is for reporting only.
When I add the device on the console manaually, I can select the type of device to other, but when I saved to finish adding, the type of device switch back to "Computer". How can I keep the type of device as other?
Management Suite isn't designed to handle assets like that. You need to look at the LANDesk Data Analytics modules with a particular focus on Asset Control as that can discover and handle non-computer assets.