It is widely recognized that next generation wireless networks will integrate heterogeneous wireless technologies. Nowadays, the borders among the different wireless network technologies are quickly disappearing. UMTS and WLAN, a popular and representative interworking paradigm, provides a plethora of multimedia services to mobile users with multimode access capability. In this paper, we propose an effective call admission control (CAC) scheme which is based on a multi- threshold bandwidth reservation scheme. Our primary goal is not to develop the optimum CAC algorithm; we want to investigate all the real future market parameters, so that the CAC mechanisms will be flexible enough to face all the possible upcoming scenarios in the next wireless generation era.