The disclosure is directed to a mobile communication device that is capable of accessing different types of networks such as a circuit-switched network and a packet-switched network. While communicating over the packet-switched network, the device negotiates a sleep interval that is longer than the ordinary interval available using the packet-switched network. In this manner, the device wakes less frequently and thereby conservers power. A buffering system is included so that data directed towards the device while it is asleep may be buffered for later delivery when the device awakens.