By default, this status option is not available in Communicator Client. However you can apply the following registry tweak to get this status option.
Steps are as follows:
1. Open registry editor and go to the following registry entry
2. Add the following key to above mentioned entry
(Type:DWORD), set value to 1 to enable status option
Now close the registry editor and restart Microsoft Office Communicator 2007, new status option should now be available.
Note: Administrators can control values of this feature via group policy settings.