\begin{pspicture}(-4,-3.2)(3,0.2)
  \psset{linecolor=lightgray}
  \pstextpath{\pscurve(-4,-2)(-2,0)(0,-3)(2,-1)(3,-2)}
             {\color{blue}
              If you want to type $3 \int^x_y = \sum^{n=1}_{33}$
              and let it follow along a curving line  \ldots}
\end{pspicture}
