Ubiquitous networking is definitely real to the mobile users; however, transparent mobility is certainly a challenge. Seamless roaming in hybrid and integrated environments demands a seamless intra-network as well as inter-network handoff mechanism for minimising any service disruption to on-going flows during switchovers. We show in this paper this could be achieved by properly managing multiple network interfaces with a handoff. We devise a client-based handoff mechanism based on the characteristics of a typical heterogeneous wireless environment by using multimode multiple network interfaces. The interface switching mechanism to minimise the power consumption is also presented. We also develop an analytical model to evaluate the performance of our proposed scheme in IP-based wireless networks. The results show that by exploiting the overlapping area between subnets and speed of mobile devices with proper management of multiple interfaces, we can significantly minimise the service disruption during handoff in heterogeneous environments.