  We study, using a monte carlo approach, the rare decay $B\to X_s \ell^+
\ell^-$ including effects of the arbitrariness of the phase between the $\psi$
amplitudes and the perturbative amplitude, $b$-quark fermi motion inside the
$B$ meson, and experimental smearing of lepton momenta. The fermi motion of
$b$-quark inside the $B$ meson is modeled by the ACCMM model. We found that
such effects reduce the sensitivities of the spectra of invariant mass and
forward-backward asymmetry of the lepton pair to new physics; especially, in
the neighborhood of the $\psi$ resonances. We also estimate the sensitivity
range of Wilson coefficients with respect to the uncertainties.
