VoIP over Wi-Fi is becoming increasingly popular. However, the high energy costs of Wi-Fi present a significant barrier to the widespread adoption of VoIP over Wi-Fi. Cell2Notify is a practical and deployable energy management architecture that addresses this issue by leveraging the cellular radio on a smartphone to implement wakeups for the high-energy consumption Wi-Fi radio. More generally, Cell2Notify provides a mechanism to send notifications to phones using an incoming call's caller ID.