As the limited IPv4 address space has made the cellular industry that decided to start using IPv6 for the mobile users in 3G-network. However, there is a potential threatto the success of 3G-network deployment, as the success will depend on the services offering to the end users. These services all reside in the current IPv4 address space,which make them inaccessible to the users that will reside in the IPv6 address space. Previous studies on network address translation have shown that the REBEKAH-IP with Port Extension, RPX is promising in that it provides excellent scalability and also supports all types of services without limitation for the mobile users in cellular network.In this paper, we propose a method that enables to evaluate and improve the performance of RPX scheme in terms of scalability and number of public IPv4 addresses utilization. Firstly, we provide a mathematical model as a guideline todetermine the range of public IPv4 addresses allocated to an RPX gateway in a cellular network. We then show architecture of RPX to incorporate with the base station of each cellular network. Therefore, RPX is able to detect the number ofmobile users’ handoff for leaving its coverage area, while the handoff detection used by RPX can be improved the scalability and the number of IPv4 addresses utilization. In addition, we present all results on the practical scalability of RPX through the mathematical analysis and simulations.