In Notes 6.5.1 and above, there is a Notes.ini setting in Windows that you can use to turn on or off the integrated instant messaging in the client.
If you have this line in your Notes.ini, integrated Instant Messaging functionality will be turned off. If you set it to IM_Disabled=0 or if you don’t have the line in your ini file at all, then the integrated instant messaging will work normally.
You can even send users a button in an email they can click to turn the functionality on or off, just put in this Lotuscript code:
Sub Click(Source As Button)
Dim s As New NotesSession
Placing a ‘1’ in the code turns OFF the IM capabilities, and placing a ‘0’ turns it back on. The user will have to restart the Notes client after hitting the button for the new settings to take effect.
Once again, this only works on 6.5.1 and above on Windows as far as I know.