This invention proposes a mobility management method and system for wireless data networks, such as GPRS and UMTS systems. The wireless data network consists of at least one mobile device and one network apparatus. The cells in a wireless data network are partitioned into several routing areas. In the wireless data network, the mobility management activities for a mobile device are characterized by a mobility management finite state machine exercised in both the mobile device and network apparatus. There are three states in the machine: idle state, standby state and ready state. Both the mobile device and network apparatus employ a ready counter, which counts the number of cells crossed by the mobile device in the packet idle period between two packet transmissions. If the counted number reaches a threshold, the mobility management state switches from the ready state to standby state.