We treat the competition between self-energy (single-micelle curvature preference) and interaction (interaggregate) effects on the evolution of micellar shapes and long-range ordering phase transitions in ternary systems of mixed surfactant and water. One surfactant prefers to satisfy the hydrophobic effect via formation of globular (positive curvature) micelles, whereas for the other we have in mind the phospholipids, for instance, which prefer to aggregate as planar bilayers. It follows that the preferred curvature in the ternary mixture case will depend sensitively on composition, i.e., on the relative numbers of the two surfactants. At high total concentrations of surfactant, however, the micellar shape is controlled as well by the relative efficiencies of packing aggregates of different curvature, independent of relative amphiphile mole numbers. By combining these self-energy and intermicellar interaction effects, then, we are able to generate "master" phase diagrams for the ternary systems, as a function of composition and concentration.