This research studies users' adoption process of WiMAX. This process cannot be viewed in isolation and must consider the effect of co-existing telecommunication networks and a highly saturated market. WiMAX success would involve getting existing mobile subscribers to switch over to WiMAX. Hence, 2/2.5G and 3G subscribers are used separately as subjects of investigation because they are likely to form the subscriber-base of WiMAX's early market and mainstream market respectively. 2/2.5G and 3G subscribers view mobile service and cost differently, hence resulting in differ in view about WiMAX. This study also shows the importance of killer applications and peer influence in the adoption process.