We study the flavor sector in models where the three families of matter are unified in a (16, 3) representation of the SO(10)×A4 group. The necessary ingredients to realize tribimaximal mixing in the lepton sector are identified systematically. The nonrenormalizable operators contributing to the fermion mass matrices play an important role. We also present a mechanism to explain the interfamily mass hierarchy of quarks and charged leptons, which relies on a "universal seesaw" mechanism and is compatible with tribimaximal mixing. © 2008 The American Physical Society.