Unbelievably unprofessional and unreliable service.  Despite calling ahead and later re-confirming the reservation time, a cab hadn't even been assigned to our 18 year old 45 minutes AFTER the scheduled pickup time.  She was left standing in the dark in a questionable neighborhood for over an hour - only to end up lucking upon a late bus to get her back to campus after an evening appointment.  Consider all other options before calling Yellow Cab; and be prepared to still have to come up with another way to get where you're going if you do decide to give Yellow Cab a try.