I. Introduction
In the past 12 months both Google [1] and Microsoft [2] as well as Research In Motion [3], Sony Ericsson [4] and Nokia [5] have opened or announced application stores targeted at smartphone applications. These stores are much like and pushed by the success of the Apple App Store for iPhone applications [6], which already has exceeded 1 billion downloads. The various application stores have rapidly filled with applications that range from the very simple to highly sophisticated ones that make effective use of the available sensors on the smartphone [7], [8].