We build an efficient and reliable data transport protocol on top of the Short Message Service (SMS). We conduct a series of experiments to characterize SMS behaviour under bursty, unconventional workloads. This study examines how variables such as the transmission order, delay between transmissions, the network interface used, and the time-of-day affect the service. We present the design and implementation of our transport protocol. We show that by adapting to the unique channel conditions of SMS we can reduce message overheads by as much as 50% and increase data throughput by as much as 545% over the approach used by existing applications. Although the transport protocol can provide efficient, low-bandwidth, moderate-latency data communication between mobile devices throughout the world, we believe that this work has the largest potential impact in developing regions where SMS is often the only option for wireless data communication.