The mobile communications market is on a continuing evolutionary path. We have seen networks go from 2G to 3G, and now the industry is preparing for 4G, such as LTE and WiMAX. While these technologies have many required changes for the radio network, the core network is also impacted. A key consideration for this migration includes the ability for a mobile subscriber to roam through the network with their multimedia services, which will require a packet core network that can manage the mobility issues. Additionally, as these new technologies are implemented operators will desire to migrate their networks and not have forklift upgrades. This will be critical in the LTE environment when the core network functions are redefined, fulfill differing requirements from today’s network. Examine the core network’s role in interworking between CDMA and LTE and CDMA and WiMAX. Explore the challenges and opportunities of roaming through these various networks as well as the impact of the LTE / SAE network standards on the core network.