This is a personal bugaboo with me too. I believe if anyone calls ME by my first name I should be able to call him/her by THEIR first name. I am on first name basis with some of the physicians at work. And there are some physicians that we address simply by their last name--"Hey, Smith...!" Obviously, these are physicians we work very closely with in ICU and have a good rapport with.
I also firmly believe, however, that when I am with a patient or introducing a physician to a patient, that the "Dr. _____" should be used. When speaking with other physicians on behalf of a doc, I also use the title...For instance in a phone call, "Hello Dr. Smith, this is Zee, RN. Dr. Johnson wanted me to notify you...."
Any young hot-shot doc that thinks he's gonna call me by my first name without giving me his/her first name is sorely mistaken. It will be Nurse Zee or Mrs. Zee...they can chose. I give a little more leeway to the docs that are older than me (these are getting fewer and fewer).