"Should of" makes me want to hurt people. Look, it's like a-whole-nother. Somewhere mid-phrase, the typist should realize that it is completely nonsensical.
What could "You should of called," possibly mean? Is it a title, like Robin of Loxley, or perhaps a unit of measure, like "bowl of cherries"? This isn't an obscure contraction. I don't see what the problem is.