The Next-Generation (NG) wireless systems are intended to unify many current systems into a seamless infrastructure, capable of offering a wide range of services to both mobile and fixed users. Planning such systems remains a challenging process which requires coping simultaneously with a large number of different aspects, such as the system performance, the network capacity, the radio coverage analysis, the signaling traffic, as well as the mobility management and the access technology. This paper presents a methodology which identifies the main planning factors and specifies the interactions between them in order to optimize both infrastructure costs and the capacity of the NG wireless systems. The main contribution resides in the identification of the parameters exchanged between each pair of modules which implement the identified factors.