Many organisations that don't want people from outside the organisation to
call certain extensions, will use anonymous calls for calls to outside the
organisation from these extensions. This however, is not a good idea;
Many people block anonymous calls. And why shouldn't they. After all an
anonymous call is like ringing someones doorbell while wearing a sky mask!
An alternative is to use a general / front desk number as a caller id. This
way, customers or patients know who are calling them without knowing the
exact extension number. Modern branch exchanges are freely programmable and
can do this for you. So except from for instance a tip line, there really
is no legitimate reason for anonymous calls.