No, there's no way to change the default subject line (this is set by the conversation code and isn't scriptable). There are a couple other ways to do this, however, using either the message class of a voice mail (IPM.Note.voice.unity) or leveraging the ViewMail form thats registered.
I ran this on my test box real quick and it works OK. Using the rules wizard on my Outlook 2000 I added a rule with the following settings:
Apply this rule after the message arrives
Where my name is in the to box (whatever criteria you want here)
Move it to the My Folder folder
Except if it uses the ViewMail for Outlook form.
You select the VMO form under the personal folders list
all incoming messages in this test got moved to the my folder folder except voice mail messages which stayed parked in the inbox.
If thats not what youre looking for, let me know and Ill dig around some more.
Jeff Lindborg
Unity Product Architect/Answer Monkey
Cisco Systems
lindborg@cisco.com
http://www.AnswerMonkey.net (new page for Unity support tools and scripts)