 It is basically very challenging to formulate one single billing method that covers all the billing schemes involved. Furthermore, 4G net- works support multimedia communications, which consist of different media components with possibly different charging units. In order to build a structural billing system for networks, several frameworks Challenges and Limitations of 4G Networks have already been studied. The requirements on these frameworks include scalability, flexibility, stability, accuracy and usability. Personal Mobility Personal mobility concentrates on the movement of users instead of user terminals, and involves the provision of personal communications and personalised operating environments. A video message ad- dressed to the mobile user, no matter where the user is located or what type of terminal is being used, will be sent to the user correctly. A personalised operating environment, on the other hand, is a service that enables other adaptable service presentations. A user also belongs to a home network that has servers with the updated user profile; when the user moves from his/her home network to a visiting network, his/her agents will migrate to the new network. 5.7.3 Quality of Service Supporting QoS in 4G networks will be a major challenge due to varying bit rates, channel character- istics, bandwidth allocation, fault-tolerance levels and hand-off support among heterogeneous wireless networks. QoS support can occur at packet, transaction, circuit, user and network levels. Packet-Level QoS This applies to jitter, throughput and error rate. Network resources such as buffer space and access protocol are likely influences. Transaction-Level QoS This describes both the time it takes to complete a transaction and the packet loss rate. Certain transactions may be time-sensitive while others cannot tolerate any packet loss. Circuit-Level QoS This includes call blocking for new as well as existing calls. It depends primarily on a network's ability to establish and maintain the end-to-end circuit. Use