Via a thin client, a first user communicates with a presence server and establishes a communication channel with a second user through the presence server. The communication channel supports instant messaging in which the first user communicates via use of a first communication protocol and the second user communicates via use of a second communication protocol. When the thin client temporarily disconnects from the presence server, the presence server maintains an active "open" session for the thin client even though the thin client is disconnected from the presence server. The thin client can reconnect to the presence server and re-establish communications over the open session, enabling the first user to again instant message the second user.