We calculate the single-particle Green's function of electrons that ar
e coupled to acoustic phonons by means of higher dimensional bosonizat
ion. This non-perturbative method is not based on the assumption that
the electronic system is a Fermi liquid. For isotropic three-dimension
al phonons we find that the long-range part of the Coulomb interaction
cannot destabilize the Fermi liquid state, although for strong electr
on-phonon coupling the quasi-particle residue is small. We also show t
hat Luttinger liquid behavior in three dimensions can be due to quasi-
one-dimensional anisotropy in the electronic band structure or in the
phonon frequencies.