Oh, goodie, a name thread!
The sad thing is, lol, T has never left me a phone message beyond the very first time we had a session, and I called him to try to get a second session scheduled and he called back. I am quite sure he would have used both first and last name, as I hardly knew him then, and he has a common first name. I feel that now, if he were to leave me a message, it would just be his first name. I had to leave him a message a couple of days ago, and I just said, "Jon, this is sunny." (not his real name) My name is not common, if it was Mary or something, I would probably use both my first and last.
We are on a first name basis, in session. He always calls me "sunny," especially when he wants me to attend to what he is saying--something important--or he is leaning in close to me and doing that look in your eyes thing. In our last session, I called him by his first name, like he does me, to get his attention. Worked great.
I don't think I would ever call a therapist "Dr." I have a Ph.D. too, so if they got all formal and wanted me to call them "Dr.", I would expect to be called "Dr." in return.
My T comes from the humanistic psychology tradition--client centered therapy, etc. I don't think therapists with that approach would put a formal title between themselves and their clients. It might be seen as not encouraging a mutualistic exchange or relationship. I think it is more of a clinical style for psychologists to want to be called Dr. Similarly, they would refer to the people they help as "patients" rather than "clients."
I love this topic....