"Correct" is dependent on style guide. :) It's used in the APA referencing style and in the Chicago Manual of Style, but I don't see a lot of call for it in scientific referencing. According to this section on Wikipedia, it seems to be a relic of an older style that's otherwise faded from English (we don't double letters for anything else now), or is a Latin abbreviation of per procurationem that has nothing to do with pages.
So far, on the wiki, it's been a matter of personal preference. Personally, I don't really see the need for "pp.", since it's always obvious when there are multiple pages, and there's no ambiguity to "p. 3–7". Nor have I felt any need to change it when someone does use it. It seems the wiki's citation templates already pick "p." and "pp." though.
If I ever get back to the FRW Style Guide, this is one of things I'd put up for a community vote or try to survey what's more common. Otherwise, we could see what's used on Wikipedia or by WotC.