No... most other operation is NOT silent. Being that MICCOM is a simplex system with an extensive system of receivers, unless you are within "x" amount of miles from a mobile unit on a truck radio or portable, you will not be able to receive them. This does not mean they are not talking. Most operations occur off the MICCOM dispatch channel, however. After dispatch, the assigned unit will utilize a secondary, tertiary, or other radio to communicate with the PSDP (Public Safety Dispatch Point) that they are enroute to.
Hope this clears that up.