The future of wireless communications will mainly focus on user centricity and personalization. Multiple networks will be overlaid to provide supplemented connectivity to a user. Competitive options in the current communication technologies need to be carefully studied for designing an interworking solution. Extensive amount of work is done on interworking of UMTS (Universal Mobile Telecommunications System) with WiFi (Wireless Fidelity). However, due to WiFi?s limited coverage it could not offer all benefits associated with interworking. With more recent technologies like WiMAX (Worldwide interoperability for Microwave Access) in the market; which offers wireless broadband access with mobility support (IEEE 802.16e), and can be deployed for a wider coverage; we can interwork it with UMTS for enhancing its performance. In this paper we present the Interworking architecture of WiMAX with UMTS. We highlight a scenario where a UMTS operator can control access of a client within two networks (UMTS, WiMAX) and port packet-data to a supportive network in the last mile. We also discuss the commercial viability for this architecture.