A messaging session is established between a first user and a second user
where messages are sent from a first user using a first device to a
second user using a second device. During the messaging session, the
second user may decide to use a third device. A presence update may be
received that specifies the third device. Messages sent from the first
user are then routed to the second user at the third device. These
messages are routed without the second user having to manually start a
new messaging session with the first user.