The Phasor Measurement Units (PMUs) will enable the state estimation of a power distribution network provided the network is observable. So far in solving the Optimal PMU Placement (OPP) problem, it was assumed that the PMUs have sufficient number of channels such that a PMU placement on any node would make all the neighboring nodes observable. This paper presents a method in which the OPP problem has been solved using PMUs with limited number of channels. The problem of combining various types of PMUs with varying costs and different channel capacity for measurement in the OPP problem has been developed and presented in this paper. Finally, the zero injection buses are included in the network when the OPP problem is solved with PMUs having limited number of channels.