Cloud Computing is emerging as the next big step in the design and deployment of an increasing number of distributed applications. Concurrent with this widespread adoption of cloud technologies, we are witnessing the emergence of mobile devices as the principal tools to accesses online services. Private, public or hybrid clouds will host many (if not most) of the online services consumed by mobile devices. Hence, cloud researchers and engineers must develop appropriate architectures and design patterns to ensure that clouds provide responsive, efficient; and feature-rich services to both native and web-based applications running on mobile devices, desktop or laptop computers. In this paper, we present Open911 as reference architecture for the development of cloud-based applications that feed mobiles devices through either native or web applications. Open911 is built on top of cloud services that run on a hybrid cloud that includes Google services and custom-built services deployed on a private cloud powered by Ubuntu Enterprise Cloud We discuss the elements of our architecture, the rationale behind our design choices, the strengths of the cloud systems, and the drawbacks or limitations that we found during our implementation effort.