Emerging input modalities could facilitate more efficient user interactions with mobile devices. An end-user customization tool based on user-defined context-action rules lets users specify personal, multimodal interaction with smart phones and external appliances. The tool's input modalities include sensor-based, user-trainable free-form gestures; pointing with radio frequency tags; and implicit inputs based on such things as sensors, the Bluetooth environment, and phone platform events. The tool enables user-defined functionality through a blackboard-based context framework enhanced to manage the rule-based application control. Test results on a prototype implemented on a smart phone with real context sources show that rule-based customization helps end users efficiently customize their smart phones and use novel input modalities.