  This is the very first paper to focus on the CR analogue of Yau's
uniformization conjecture in a complete noncompact pseudohermitian
$(2n+1)$-manifold of vanishing torsion (i.e. Sasakian manifold) which is an odd
dimensional counterpart of K\"{a}hler geometry. In this paper, we mainly deal
with the problem of the sharp dimension estimate of CR holomorphic functions in
a complete noncompact pseudohermitian manifold of vanishing torsion with
nonnegative pseudohermitian bisectional curvature.
