You're right, with one clarification: Miss. isn't an abbreviation, it's the full word. Ms. is short for Miss but is used for professional communication nonetheless. [Source: I transcribed documents intended for lawyers]
Huh, I guess I never stopped to think what "Ms." is short for, and it very well could be "Miss". However, for those non-native English speakers on HN, it's pronounced differently: "Miss" is pronounced with an unvoiced "s" at the end, "Ms." is pronounced "Mizz".
Actually I take it back! Ms. isn't short for "Miss". Miss (no period) used to be the default title for a woman, but now it's Ms. (pronounced as you say), and like Mrs. & Miss, derives from Mistress.