Although cellular networks such as GPRS (2.5G) or UMTS (3G) have achieved providing both circuit-switching and packet-switching services with wide area coverage, the mobile users are still expecting higher rates and more mobility to satisfy their needs. Integrating current network architecture with other high-speed and low-cost wireless technologies is a key challenge for migrating to 4G. The IEEE 802.11 technology which has been well-developed and widely-used in local area networks seems to be a proper choice for fulfilling users' expectations. Its ad hoc functionality further improves the mobility of the users.This research proposes an architecture to achieve the internetworking between 802.11 Mobile Ad Hoc Network (MANET) and UMTS. The key approach being applied for intersystem handovers is SGSN signaling and for ad hoc mobility management is the Mobile IP signaling. The main purpose of this research is to retrieve the best effects by integrating these two network technologies. The integration system results several important features: wide area coverage, mobility and quality of service management.