Abstract:          The greater bandwidth provided by wireless LANs can be a precious asset to the wireless ubiquitous computing if the integration with 3GPP systems is done at a certain level. This paper presents a proposal to integrate wireless systems at core network level. Service integration becomes very powerful and easy. The system is not so dependent on the critical latency of vertical handovers and the users feel a unique system providing services. Little changes are required to the current 3GPP core network. Our architecture uses the GPRS as the primary network and integrates WLANs as secondary networks, used on an availability basis. Sessions on secondary networks survive disconnection periods contributing to a seamless service provision to the user. The paper describes the overall architecture, the changes that are needed at the current 3GPP core, and the operation of the secondary networks on the aspects of data routing and security associations. Highlights about the application model are presented at the end.