This paper studies the multi-area voltage and reactive power management regarding the voltage stability. In this respect, the maximization of effective reactive power reserve is proposed using centralized and decentralized implementations. The proposed formulations benefit from the detailed modeling of generators reactive power limits as well as the distributed slack bus model for the compensation of active power imbalances. In addition, the generator switch between the constant terminal voltage and the constant reactive power output is modeled by the complementarity constraints. The simulation results demonstrate that the well-known decentralized implementation does not converge whenever there are PV generators at border buses. It is illustrated that this problem occurs when the complementarity constraints are considered. Appropriate modifications are proposed for the formulation of the decentralized optimization in order to consider the effect of the complementarity constraints at border buses. The effectiveness of the proposed formulation to handle such optimization problems is evaluated using the New England 39-bus system with three areas.