If so, my analysis amounts to a rule in search of actual usage—a prescription rather than a description. In any event, the impressive rise of "free of" against "free from" over the past 100 years suggests that the English-speaking world has become more receptive to using "free of" in place of "free from" during that period.
The fact that it was well-established long before OP's 1930s movies is attested by this sentence in the Transactions of the Annual Meeting from the South Carolina Bar Association, 1886 And to-day, “free white and twenty-one,” that slang phrase, is no longer broad enough to include the voters in this country.
I don't think there's any difference in meaning, although "free of charges" is much less common than "free of charge". Regarding your second question about context: given that English normally likes to adopt the shortest phrasing possible, the longer form "free of charge" can be used as a means of drawing attention to the lack of demand for ...
With the advent of the free software movement, license schemes were created to give developers more freedom in terms of code sharing, commonly called open source or free and open source software.
I want to make a official call and ask the other person whether he is free or not at that particular time. I think asking, “Are you free now?” does't sound formal. So, are there any alternatives to...
My company gives out free promotional items with the company name on it. Is this stuff called company swag or schwag? It seems that both come up as common usages—Google searching indicates that the
Similarly, “free education” is funded by the state (which is ultimately financed by taxpayers) and taught in state-run schools called state schools whereas schools that charge tuition fees are termed private schools. A private school in the US typically means fee-taking. Confusingly, in the UK, they are known as public schools.
In the context such as "free press", it means libre from censorship, "gluten-free" means libre from gluten and so on. Then there is "free stuff", why is the same word used?