Free ride dates back to 1880, while free loader is a more recent construction “freeloader (n.) also free-loader, by 1939, from free (adj.) + agent noun from load (v.)As a verb, freeload is attested by 1967 and probably is a back-formation from this”
I checked Garner's Modern American Usage; although BG doesn't address free of vs. free from, he writes that the distinction between freedom of and freedom from is that the former indicates the "possession of a right" (freedom of speech) and the latter "protection from a wrong" (freedom from oppression). So free from is used to indicate protection from something problematic, and free of (which ...
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 ...
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...
1 ' Free ' absolutely means 'free from any sorts constraints or controls. The context determines its different denotations, if any, as in 'free press', 'fee speech', 'free stuff' etc.
Free entrance X chargeable entrance. Free parking X paid parking. Free service X chargeable service. Free consultation X paid consultation. Free health care X expensive health care. Free toilet X pay toilet. Free fare (in the sense of a free ticket to travel, the opposite can be a paid ticket). Here there is a mentioning of paying a ticket fare.