The mobile computing functions can be logically divided into following major segments (Figure 1.1): 1. User with device: The user device, this could be a fixed device like desktop com-puter in office or a portable device like mobile phone. Example: laptop comput-ers, desktop computers, fixed telephone, mobile phones, digital TV with set-top box, palmtop computers, pocket PCs, two way pagers, handheld terminals, etc. 2. Network: Whenever a user is mobile, he will be using different networks at dif-ferent places at different time. Example: GSM, CDMA, iMode, Ethernet, Wireless LAN, Bluetooth etc.