Instant Messaging stores configuration settings in the iim.conf file within the Configuration Directory (im-cfg-base).
On Solaris:
/etc/opt/SUNWiim/default/config/iim.conf
On Linux:
/etc/opt/sun/im/default/config/iim.conf
If you created multiple instances of Instant Messaging, the name of the /default directory will vary depending on the instance. See Creating Multiple Instances from a Single Instant Messaging Installation for more information.