Energy efficiency is a primary design criterion of the modern Smartphone due to limitations in battery capacity. Multi-core processors are now commonplace in these devices, which adds a new dimension, the number cores used, to energy management. In this paper, the authors investigate how the mechanisms of frequency scaling and core off-lining interact, and how to use them to reduce energy consumption. They find surprising differences in the characteristics of latest-generation Smartphone's, specifically in the importance of static power. This implies that policies that work well on one processor can lead to poor results on another.