Need to use \pageref to a page that has *-equations

It suffices to place the \label "anchor" somewhere on the page you need to cross-reference. Just don't place the label inside an environment which, by design, won't take a numbering anchor.

To minimize the chances that an unfortunate page break will happen between the equation and the label (and therefore not getting the page reference right), be sure to place the \label instruction immediately before the equation whose page number you want to cross-reference. As @egreg has pointed out in a comment, that's a safe placement option, because inserting a page break immediately before a display equation isn't a legitimate move for LaTeX.

The following MWE

\documentclass{article}
\begin{document}
\label{page:emc2}  % place the \label instruction immediately before the unnumbered equation
\[  % an unnumbered display-style equation
E=mc^2
\]
\clearpage
A famous equation is shown on page \pageref{page:emc2}.
\end{document}

produces this output on page 2:

A famous equation is shown on page 1.

You can use the standard \label command in disguise:

\documentclass{article}
\usepackage{amsmath}

\makeatletter
\let\pagelabel\ltx@label
\makeatother

\begin{document}
\begin{align*}
E&=mc^2\pagelabel{page:emc2}\\
F&=nd^2
\end{align*}
\clearpage
A famous equation is shown on page \pageref{page:emc2}. 
Which one, you will ask? Indeed, it is a puzzle for the readers
to solve.

\end{document}

However, it's better either to \tag the equation or to number it, for the reason I add in the code above.