In this paper smartphones are discussed. Today's smartphone are more common than computers. In fact, smart phones are simply computers with extra hardware-namely, a GSM (Global System for Mobile Communications) radio and a baseband processor to control it. These extra features are great, but with the power they provide, there's also a threat. Today, smartphones are becoming targets of attackers in the same way PCs have been for many years. This paper focus on the security models of two smart phone operating systems: Apple's iOS and Google's Android. These two have a special place in my heart because I was the first to publicly exploit both of them.