Answer:

In the business world it is always better to “phone ahead” to be sure that you will not arrive just as the person is beginning an executive conference from which he or she cannot escape. It is reasonable to “drop by” to leave something with a secretary or pick up something, but do not expect your contact to appear.

Doctors, dentists, and beauticians also operate on the appointment system, so do not expect to go to the office or shop and just wait for your turn.