In this paper, we are interested in the interconnection between an ad-hoc network and UMTS system. In presence of two access technologies, new challenges arise and mobile host will have face multiple base stations or gateways with different utilizations. As a result, a user who needs to establish a voice call, prefers to be connected through UMTS and a user who needs to transmit a Best Effort traffic with high rate, prefers to be connected through ad-hoc network. The aim of that combination is to improve the coverage of cellular networks and increases the services which can be made available for mobiles. This combination also reduces transmission power for mobile hosts. Our main result is characterization of stability condition and the end-to-end throughput using the rate balance. Numerical results are given and support the results of the analysis. Finally, we perform extensive simulation and verify that the analytical results closely match the results obtained from simulations.