  Exploiting continuity properties of Fourier multipliers on modulation spaces
and Wiener amalgam spaces, we study the
  Cauchy problem for the NLW equation. Local wellposedness for rough data in
modulation spaces and Wiener amalgam spaces is shown. The results formulated in
the framework of modulation spaces refine those in [3]. The same arguments may
apply to obtain local wellposedness for the NLKG equation.
