As wireless technologies continue to advance, mobile users have developed a need for ubiquitous accessing to the Internet while roaming among heterogeneous wireless net- works. Guaranteeing service continuity requires an effective mechanism to optimally use all available access networks. In order to achieve this goal, applications need to handle transient network outage and react accordingly to retain ongoing services. Applications with such capability require expert programmers to make huge efforts on many details that are totally irrelevant to application logic. In this paper, we propose Heterogeneous Network Communication System (HNCS), which is an Android platform that provides always- best-connection and service continuity for applications. Fur- thermore, HNCS allows programmers to easily implement applications that are invulnerable to transient network changes. The experiment results show that HNCS meets the goal of maintaining service continuity when roaming among heterogeneous networks.