In this paper, we investigate how smartphone applications, in particular web browsers, are used on mobile phones. Using a publicly available widget for smart phones, we recorded app usage and the phones' acceleration and orientation from 1,330 devices. Combining app usage and sensor data we derive the device's typical posture while different apps are used. Analyzing motion data shows that devices are moved more while messaging and navigation apps are used as opposed to browser and other common applications. The time distribution between landscape and portrait depicts that most of the landscape mode time is used for burst interaction (e.g., text entry), except for Media apps, which are mostly used in landscape mode. Additionally, we found that over 31% of our users use more than one web browser. Our analysis reveals that the duration of mobile browser sessions is longer by a factor of 1.5 when browsers are explicitly started through the system's launcher in comparison to being launched from within another app. Further, users switch back and forth between apps and web browsers, which suggest that a tight and smooth integration of web browsers with native apps can improve the overall usability. From our findings we derive design guidelines for app developers.