In heterogeneous wireless networks, there have been several efforts aimed at having mobile devices equipped with multiple interfaces connect optimally to the access network that minimizes their power consumption. However, a study of existing schemes notes that in the idle state, a device with both a WLAN and a WWAN interface need to keep both interfaces "on" in order to receive periodic beacon messages from the AP (WLAN) and downlink control information from the base station (WWAN), resulting in significant power consumption. Therefore, in this paper, we propose a Power-efficient Communication Protocol that includes turning off the WLAN interface after it enters the idle state and using the existing paging of WWAN in order to wake up the WLAN interface when there is incoming long-lived multimedia data. Further, we propose turning on the WLAN interface when the number of packets in the radio network controller's buffer reaches a certain threshold level in order to avoid repeatedly turning on and off WLAN interfaces, that consumes a significant amount of power. The tradeoffs between the power saving and the number of packets dropped at the buffer are investigated analytically. Simulation results for scenarios of interest are also provided.