The incorporation of contextual elements of location, time, and identity into traditional computer and network systems and services is resulting in enhanced, intuitive, more natural user experiences. This work defines an instance of a presence-based messaging system called Pebbles and Urns. A survey of current messaging systems has indicated key missing elements that are addressed by functionality in the Pebbles and Urns architecture. Current context-based messaging research focuses on the social activities and social interactions of the user. While that is important, this work proposes how Pebbles and Urns would augment the numerous ways a person deploys, obtains, and realizes information in their daily activities. Next, it considers agent design and tuplespaces as implementation components of Pebbles and Urns. An agent's ability to react to context, combined with tuplespace characteristics of distributed, associative memory, persistent storage, and destination - space - time uncoupling allow the investigation of new messaging schemes offering interesting advantages over existing messaging systems. This work closes with several Pebbles and Urns user scenarios and suggested future work to extend the Pebbles and Urns messaging system.