I think Twik said most of it for me. Ms. can be used for any woman -- that is the point. As a seventies feminist who never changed her name despite a long and happy marriage, I don't like being called "Mrs." I think those who do it see it as a mark of respect for an older woman, but we are the women who made it possible for your marital staus to be private, for you to call yourself whatever you like, work at the profession of your choice, get into college on merit, and even attend the college of your choice. I fought for Ms.
If you don't know I can be called "Dr.", call me "Ms.", not "Mrs." And certainly not "White." I am definitely a grown-up and deserve to be treated as one. Also, suppose my given name was, in full formality, Elizabeth, but I am always called Betsy. When you start calling me "Elizabeth" you are insisting on calling me by a name I do not use. If you actually knew me well enough to call me by my given name, you would know if it was Theresa, Tess, Terry or Spike. If you don't know my preferred form of address among my friends, you do not know me well enough to call me anything but Ms., or Dr., Lotus. Yes, there is a first-name informality among colleagues and even socially, but in business relationships, or as a general rule, it presumes too much.