Currently, communication technologies have been experiencing significant development. It has been expected that traffic from mobile devices will grow abundantly in the near future. WiFi offload has become one of the solutions to overcome the problem of traffic density. In this paper, offloading LTE network to WiFi (802.11g) network is of interest. One of the major issues existing in the LTE - 802.11g offload is the dropped call which occurs in the handoff process. In this paper, we propose to use a modified coalition game theory approach to obtain a smaller number of dropped calls in the vertical handoff. Simulation results show that the proposed method successfully provides a smaller number of dropped calls compared with the conventional method. In particular, by using our proposed method, the number of the dropped calls reduces by 5.57% compared with the conventional method. Additionally, it provides more reduction, i.e. by about 34.64%, when six 802.11g user nodes are used.