How to have roman pagenumbering, then arabic pagenumbering, without resetting the page number?

(The title and body of the posting are about two different things. I've chosen to answer the question raised by the body of the posting.)

You need to place pagenumbering{roman} immediately after begin{document}. E.g.,

documentclass{article}
usepackage{lipsum} % filler text
begin{document}

pagenumbering{roman}

thispagestyle{empty} % don't show page number (i)
lipsum[1]            % stuff on page `i' / 
clearpage

thispagestyle{empty} % don't show page number (ii) 
lipsum[2]            % stuff on page `ii' 
clearpage            

lipsum[3]            % stuff on page `iii' // page number IS shown
clearpage

bla bla bla           % rest of document

end{document}

It seems that you want a book, were as usual, the main matter pages have arabic numbers while front pages have roman numbers, except the page title, that obviously do not need any numeration.

If this is true, well... then just make a book with the scrbook class, add a front matter with a tittle, and finally a main matter with chapters o whatever, but without messing with page counters:

documentclass[article]{scrbook}% or documentclass{book} 
% usepackage{clrdblpg} % for book only 
title{foo}
begin{document}
frontmatter
maketitle       % Title page (i) and blank page (ii)
tableofcontents % page iii and blank page (iv)
mainmatter
chapter{bar} % page 1 and blank page (2)
chapter{baz} % page 3
end{document}

With the standard book class the blank pages have the same numeration, but numbers are not suppressed in blank pages. Using usepackage{clrdblpg} the result will be the same at this respect.