1. A method of using a mobile device to communicate with a cellular network, the mobile device comprising a baseband processor and an applications processor, the method comprising: by the applications processor: generating a keep-alive packet; providing the keep-alive packet to the baseband processor; and entering a sleep mode to conserve power of the mobile device, wherein the baseband processor is configured to send the keep-alive packet over a data connection between the mobile device and the cellular network while the applications processor is in the sleep mode.