  We analyze a class of supersymmetric SO(10) grand unified theories with type
II seesaw for neutrino masses, where the contribution to PMNS matrix from the
neutrino sector has an exact tri-bi-maximal (TBM) form, dictated by a broken
S_4 symmetry. The Higgs fields that determine the fermion masses are two 10
fields and one 126 field, with the latter simultaneously contributing to
neutrino as well as charged fermion masses. Fitting charged fermion masses and
the CKM mixings lead to corrections to the TBM mixing that determine the final
PMNS matrix with the predictions theta_{13} ~ 4-6 degrees and the Dirac CP
phase to be between -10 and +15 degrees. We also show correlations between
various mixing angles which can be used to test the model.
