Suppress introductory page numbers

The warnings are probably caused by hyperref, because you're not generating the page numbers that the package needs for setting anchors. It's probably better to redefine the page style for frontmatter to empty:

\documentclass{memoir}
\usepackage{hyperref,kantlipsum,etoolbox}

\makeatletter
\aliaspagestyle{title}{empty} % suppress the page number after \maketitle
\let\origps@chapter\ps@chapter
\preto\frontmatter{\let\ps@chapter\ps@empty\pagestyle{empty}}
\preto\mainmatter{%
  \cleardoublepage
  \let\ps@chapter\origps@chapter\pagestyle{headings}}
\makeatother

\begin{document}

\frontmatter
\title{My Book}
\author{Me}
\maketitle

\tableofcontents*

\chapter{Intro}
\kant

\mainmatter

\chapter{First}
\kant
\end{document}

Change headings into mystyle if you want to use this one in the main matter.

---

Personally I find it a bad idea to suppress page numbers: every page should have a printed number, in order to help the reader in consulting the document. Only some special pages may be an exception (dedication or colophon, for example, but not an introduction). But this depends on the document, of course; if the frontmatter consists only of a title page and a one page table of contents the page numbers are probably not necessary. If the frontmatter has table of contents, list of figures and other material such as a preface, the pages should be numbered, in my opinion.

Memoir provides \aliaspagestyle{}{} for this purpose:

\documentclass{memoir}
\begin{document}

\frontmatter
\pagestyle{empty}
\aliaspagestyle{chapter}{empty}
\title{My Book}
\author{Me}
\maketitle

\mainmatter
% \aliaspagestyle{chapter}{ruled}
\pagestyle{ruled}% <-- for example
\chapter{A Chapter}
Some text.

\end{document}