Student or Learner
For quite a long I have been wondering about how to express this type of numbers. For example a number like this; "2590 OR". We surely know that 4th number is Zero(in AmE) or O (in BrE alphabet). If it is written in paper it can certainly be recognized but when you listen to it when expressing it in BrE, it is quite tricky. I can't catch up it. In BrE, the whole numbers might be read as "two, five, nine, O, O, R". I definitely would write both 4th and 5th numbers either in number or alphabet.
I don't think there is anything distinctly American or British about calling the number zero "oh" in informal contexts.
In a situation like you describe, where there are mixed letters and numerals in something like a "part number" or "model number" then you have to be explicit.
You have to say "zero" for zero and "oh" for O.