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.
(..) another listing, new, around the corner. - Yeah? - Yeah. - Hi. - Hi. - It's by appointment only. - Oh, well, I'm here to see the owner. He's in the recreational vehicle. Yo, it's appointment only. How are you feeling? About as good as you look. (..)2008 TvShow: Breaking Bad Title: A No-Rough-Stuff-Type Deal Season: 1 Episode 7