For your purposes, turning the DBMS flag off and rebooting the system should be sufficient to wipe the DB
I don't believe this would wipe the voicemail partition however (potentially a much more important factor)
There is a way to format the hard drive but that would require physical access to the Maintenance port via serial cable (no, telnet to port 2002 will not do)
You might be able to use the SWI tool to perform a full install without restoring the DB afterwards if you can't manage the Maint port method.
If SWI and Maint port options are not avail, I would use a FTP client like filezilla to delete all of the messages off of the /vmail partition and then use the DBMS flag off.
Pulling the hard drive would be best IMO
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