  In cond-mat/0306131 Huang {\em et al.} reported for the first time a
numerical evidence for the predominance of small phonon momenta in the
electron-phonon coupling induced by electronic correlation. They report also an
upturn of the electron-phonon vertex function for small momenta as function of
the Hubbard repulsion $U$ for sufficient large $U$. In this comment we compare
their Quantum Monte Carlo data with analytical results based on slave-boson
techniques for generic $U$. We associate the upturn of the electron-phonon
vertex function with the tendency towards a phase separation instability at
large temperatures.
