The document proposes a scalable mobile presence cloud architecture called "presence cloud" to address scalability issues in large-scale mobile presence services. Presence cloud distributes user information across multiple presence servers organized in a quorum-based structure. It uses a directed buddy search algorithm and caching to achieve low latency buddy searches. Analysis shows presence cloud reduces the number of messages needed for searches compared to alternative architectures like mesh-based or distributed hash table approaches. The presence cloud architecture can enable efficient and scalable mobile presence services for large social networks.