During the last years, the mobile cellular networks have evolved from pure voice telephony networks to universal data networks. The so-called first generation of mobile networks, that means the analog systems like for example AMPS or TACS, provided circuit switched point-to-point connections between two users for voice services. The second generation, mainly known through the GSM system, provides additional capabilities for point-to-point data transmission, at comparably low bit-rates. However, with the evolution of second generation systems, visible for example in the GPRS technology, and with the introduction of 3G systems like UMTS, Internet technology like the use of IP protocols has been introduced into mobile networks, together with radio technology that provides higher data rates for the end user. Thus, evolved 2G and 3G systems offer possibilities and services previously only known from the Internet, and extend Internet access to mobile users. Mobile users now have access to Internet services like e-mail, web browsing, and to mobile services like multimedia messaging (MMS). MMS also allows exchange of messages to and from the Internet. In other words, Internet services become usable for mobile users, and mobile services like MMS become usable for Internet users. Thus, the Internet really extends to mobile users.