Sensor networks are emerging wireless technologies; their integration with the existing 2.5G, 3G mobile networks is a key issue to provide advanced services, e.g., health control. However this integration poses new challenges in the design and simulation of the involved embedded systems since it requires the cooperation of simulation tools that model hardware, software, and network aspects and their interactions. We present the modeling and simulation of a network scenario, core of a telecom provider’s future portfolio, in which an ARM-based mobile handset is used as the gateway between a wireless sensor network (WSN) and remote users through a wide area network (WAN). Initially, the gateway and the WSN are modeled at system level with SystemC while the wide area network is modeled with NS2. Then, HW/SW partitioning is performed on the gateway and an instruction set simulator of the ARM processor is used for the cycle-accurate execution of the RTOS and the application software.