  We present a scenario which naturally provides bi-maximal neutrino mixings
for a simultaneous explanation of the recent atmospheric and solar neutrino
data. A crucial role is played by an anomalous flavor ${\cal U}(1)$ symmetry,
which is also important for a natural understanding of charged fermion mass
hierarchies and magnitudes of the CKM matrix elements. Within MSSM the solar
neutrino problem can be resolved either through vacuum oscillations or the
large mixing angle MSW solution. In supersymmetric GUTs such as SU(5) and
SO(10) the MSW solution is realized. If the flavor ${\cal U}(1)$ also mediates
supersymmetry breaking, the vacuum solution in MSSM is eliminated, and only the
large mixing angle MSW solution survives.
