Despite the rapid hardware upgrades, current smartphones suffer various unpredictable delays during operation, e.g., when launching an app, leading to poor user experience. In this work, we investigate the behavior of reads and writes in smartphones. We conduct the first large-scale measurement study on the I/O delay of Android using the data collected from our Android app running on 1009 devices within 130 days. Among other factors, we observe that reads experience up to 626% slowdown when blocked by concurrent writes for certain workloads. We use this obtained knowledge to design a pilot solution called SmartIO that reduces application delays by prioritizing reads over writes. SmartIO is implemented on the Android platform and evaluated extensively on several groups of popular applications. The results show that our system reduces launch delays by up to 37.8%, and run-time delays by up to 29.6%.