Enumerate label numbers

This is almost the same answer, but with safe reference to label names instead of item numbers (i.e., when the item order is changed, the references are still correct).

\documentclass[]{beamer}
\usetheme{Warsaw}
\setbeamertemplate{items}[circle]
\usepackage{tikz}

\newcommand*\itemref[1]{%
\tikz[baseline=(char.base)]{%
\node[circle, fill=enumerate item.fg, inner sep=.6pt] (char) {\scriptsize\color{white}\ref{#1}};}}

\begin{document}

(Compile twice to solve the cross references).  

\begin{frame}
\frametitle{Example}
\begin{enumerate}
\item \label{one} First one
\item \label{two} Second one
\item  Last minuted included item without importance 
\item \label{three} Third one
\end{enumerate}
In the above list, \itemref{one}, \itemref{two} and \itemref{three} are the more important.

\end{frame}
\end{document}

For sake of completeness, I believe the best solution is the combination of @Markus and @Fran. References to item labels with templated markers:

\documentclass[]{beamer}
\usetheme{Warsaw}
\setbeamertemplate{items}[circle]
\usepackage{tikz}

\newcommand\itemref[1]{{\renewcommand{\insertenumlabel}{\ref{#1}}%
  \usebeamertemplate{enumerate item}}}

\begin{document}

(Compile twice to solve the cross references).  

\begin{frame}
\frametitle{Example}
\begin{enumerate}
\item \label{one} First one
\item \label{two} Second one
\item  Last minuted included item without importance 
\item \label{three} Third one
\end{enumerate}
In the above list, \itemref{one}, \itemref{two} and \itemref{three} are the more important.

\end{frame}
\end{document}

If the appearance is the only thing matters, then the following will do:

Code

\documentclass[]{beamer}
\usetheme{Madrid}
\setbeamertemplate{items}[circle]
\usepackage{tikz}

\newcommand\mynum[1]{%
  \usebeamercolor{enumerate item}%
  \tikzset{beameritem/.style={circle,inner sep=0,minimum size=2ex,text=enumerate item.bg,fill=enumerate item.fg,font=\footnotesize}}%
  \tikz[baseline=(n.base)]\node(n)[beameritem]{#1};%
}

\begin{document}

\begin{frame}
\frametitle{Example}
\begin{enumerate}
\item First one
\item Second one
\item Third one
\end{enumerate}
In the above list, \mynum{2} and \mynum{3} are what more important.
\end{frame}

\end{document}

Output