These are calls from the San Francisco Ballet - they are fundraising for Dance in the Schools and Communities with a matching grant from PG & E. Their policy is to not leave a message, hoping you do not have caller ID. Until they go to Second Life or learn to Tritter, this is the only way they can do their job.
865-2000 is the box office, 865-6791 goes to an unmanned answering machine, and 865-6790 will get you a real human being, who can answer any questions.