In this paper, we describe the development of a GSM-derived regional mobile satellite communication system. We first discuss the market needs of a regional mobile communication system, and stress the technical requirements for such a system to be successful in the commercial world. We then point out the advantages of deriving such a system from the popular GSM standard and discuss the similarities and differences between the two systems. We then describe a system designed by Lockheed Martin Corp., known as ACeS, which serves the telecommunication needs of Asia. The ACeS system works in both the cellular and satellite environments and is designed to make optimal use of the similarities and differences to the GSM system. We end the paper by discussing some challenges in the evolving area of mobile satellite communication systems