Starting with the pre-interview e-mails and then Skype interview to get into the school, the faculty referred to themselves by first name. Now I am here, and everyone goes by first name. Other faculty in the department, including the professor I'm TAing for, whose position is one of a senior instructor but not someone I'll have for my own classes, I'm not sure about, because I haven't met her yet. I addressed her as Dr. So-and-so in an e-mail, but she didn't respond back to me to know what to call her. At another school I interviewed at, the professors never indicated that I should refer to them by first name, and grad students there didn't refer to them by first name until later into their program.