  The observed orbits of extrasolar planets suggest that many giant planets
migrate a considerable distance towards their parent star as a result of
interactions with the protoplanetary disk, and that some of these planets
become trapped in eccentricity-exciting mean motion resonances with one another
during this migration. Using three-dimensional numerical simulations, we find
that as long as the timescale for damping of the planets' eccentricities by the
disk is close to or longer than the disk-induced migration timescale, and the
outer planet is more than half the mass of the inner, resonant inclination
excitation will also occur. Neither the addition of a (simple, fixed) disk
potential, nor the introduction of a massive inner planetary system, inhibit
entry into the inclination resonance. Therefore, such a mechanism may not be
uncommon in the early evolution of a planetary system, and a significant
fraction of exoplanetary systems may turn out to be non-coplanar.
