  We study the evolution of fronts in the Klein-Gordon equation when the
nonlinear term is non-homogeneous. Extending previous works on homogeneous
nonlinear terms, we describe the derivation of an equation governing the front
motion, which is strongly nonlinear, and, for the two-dimensional case,
generalizes the damped Born-Infeld equation. We study the motion of one- and
two-dimensional fronts, finding that the dynamics is richer than in the
homogeneous reaction term case.
