Mobile devices are becoming ubiquitous. There is an explosion worldwide in the use of handheld electronic communication devices, such as mobile phones, digital music players, and handheld Internet access devices. As the number of such devices is multiplying, subscriptions to services offered through these devices are expanding.1 The number of such subscriptions worldwide grew at a compounded annual rate of 24% from 2000 to 2008 with the number of mobile subscribers reaching 4 billion in December 2008 (International Telecommunications Union 2008).