Since there seems to be a lot of misinformation here, let me put in my two cents.
The general consensus in the American business world in my experience, and according to my Honors English instructor, seems to be that Ms. is pronounced "Miss" and should be used as the generic reference to any female whenever her marital status is not know, and also if it IS known that she is NOT married. Also it does not matter if she is divorced, she is still a "Miss/Ms.", as it is impolite to title her by the fact that she is divorced. The only time when one can't be certain about the correct title is when the woman is widowed, in which case it depends upon her preference. Some widowed women like to go back to being called a "Miss/Ms." while others prefer to remain a "Misses/Mrs." This seems to depend somewhat upon whether or not the woman is interested in remarrying.
Mrs. means "Misses" and refers specifically and ONLY to a married woman.
Mz. is the only abbreviation that would be pronounced "Mizz" but it is archaic and is realistically never used anymore. In 12 years working in offices and customer service, I have NEVER even once seen Mz. used.
Also, nobody in America uses the term "master" for young men. This is also considered archaic and even arrogant by some. Young men are referred to as Mr., just as all men are.
I'd prefer if we just changed all the rules and used the simple "Mr" or "Ms" ALL THE TIME but old rules die hard.