A persistent personal messaging system provides shared memory space functionality supporting a user changing between a plurality of client devices, even within a loosely coupled, distributed system for persistent personal messaging. A user, irrespective of which messaging client they are using, logs on to the system. The act of logging on places user data, representing the user, into the shared memory space. A “contacts” service agent finds the friends and groups that the user belongs to and notifies other users that the user has logged on. Given the on-line status of other users and groups, a “history” service agent will retrieve previous messages from the shared memory space that formed the user's conversations with users and groups, as if the user had never logged off or switched devices. When the user adds a new message to any conversation, the message is added to the shared memory space.