The complexity of modern mobile phones makes it difficult for developers to understand the power consumption of their applications. Our measurement framework produces fine-grained, annotated traces of a phone’s power consumption which we are using to develop an understanding of how particular aspects of an application drive energy use. We ran a large number of automated tests using Google Android G1, Magic, Hero and Nexus handsets and present results for the average energy consumption of connection and data transmission over 802.11 wireless networks. Our results show that the optimal choice of data transmission strategy is different between handsets, operating systems, and device context.