The next generation mobile devices will be enabled with the ability to support multiple types of networks i.e. the terminal supports multiple network interface. The key enabling function for achieving seamless mobility and seamless service continuity for such devices is seamless handoffs across heterogeneous wireless access networks. A challenging issue in the multi-service Next Generation Wireless Network (NGWN) is to select the appropriate handover decision strategy for the handover initiation stage. An overview and categorization of various vertical handoff decision schemes are shown that helps in selection of best scheme among them all accordingly to the requirements of different users.