QuickBooks Messenger is activated by being in Multi-User mode and in QuickBooks you can disable and enable the messenger by performing the following:
To disable the QuickBooks Instant Messenger feature: In multi-user mode, sign in as Admin. Go to File/Utilities. Disable QuickBooks Messenger. Log out of the company file and then log back in for the setting to take effect Of course, to enable the Messenger, step 3 would be to "Enable QuickBooks Messenger".