Omitting the “hundred” from the name of numbers

I’m not a native, so I’ve always spoken numbers in English as our textbooks tell us to do: 452 would be “four hundred (and) fifty-two.” But I’ve recently heard natives say something like “four fifty-two” in a couple of movies. (The numbers could be different.)

Is this grammatically correct? Is it common in informal speech? What about formal speech? Can it be used in formal contexts?

Also does this usage depend on the context? Or can you use this system in any setting? I remember at least once (in the movie Get Smart) this style was used to refer to the number of a page (from a report). But I’m sure I’ve heard it in another context too. I just can't remember what.

I couldn't find the answer myself, mostly because I didn't know what to search.

By the way, I’ve been taught US English, but I’d like to know the UK usage too (in case there is any difference here).

Thank you in advance.

In informal speech, we sometimes take shortcuts when saying numbers.

Three-digit numbers can be said as 1-23, “one twenty-three”.

Four-digit numbers can be said as 12-34, “twelve thirty-four”.

In both cases, if the tens digit is a zero, you must say “oh” for that digit: 103 is “one oh three” and 1204 is “twelve oh four”.

If the tens and ones digits are both zero, you say “hundred”: 1200 is “twelve hundred”. I think I’ve read this is not allowed in BrE, but it’s very common in AmE.

It’s less common with five or six digits, but you could say 12,345 as 12-3-45 and 123,456 as either 1-23-4-56 or 12-34-56.

Do not do this in formal speech; say the full number.