We are calling to 'confirm your appointment' with Dr. Jones. = We are calling to make sure that you will 'keep your appointment' with Dr. Jones.
The museum is open to visitors 'by appointment' only. [=you have to make an appointment to visit the museum]
The court ordered the 'appointment' of an attorney to represent the child.
(..) - Time to talk to Mr. Fox, I think. - I'll get 'im on the phone. No, no, no, no, no. Do we still have any cars... around the place? Yes. One or two. I need an appointment at the hospital for my leg. - Which hospital? - Whichever one Jim Gordon's in. - I have seen worse cartilage in knees. (..)2012 The Dark Knight Rises