The convergence of existing wireless communications evolves to all Internet Protocol (IP)-based networks with several services. We focus on integration of Universal Mobile Telecommunications System (UMTS) and Wireless Local Area, Network (WLAN) environment. However, the transmission capacity difference of two networks causes the seamless mobility, secure connection, and the real-time charging difficulty. Moreover, there are still several problems such as Vertical Handoff (VHO), security, roaming, Quality of Service (QoS), accounting, billing and charging. In this paper, we describe service-oriented issues for mobility, security and billing in mobile next generation networks (NGNs). In additional, we propose mobility and charging solutions for integrated system management using a Mobility Manager (MobiM) and Charging Manager (CharM) in mobile NGNs. Thus, we solve the problems of seamless mobility and real-time charging in integration of UMTS and WLAN environment.