You've always been able to do that, haven't you?
Here's how:
Create no-ring dummy-number key appearances on a spare multiline set port. (the physical instrument does not even have to exist). You can even program up a dummy PKM or two on that same non-existent instrument to really get a bunch of blank spots to fill.
Next assign the digit star (*) plus the extension number of each user that you want to be able to do this for. Example if you have exts assigned to (Lawyers) on ext 1001, 1002 and 1003 (I could go on....) simply create dummy numbers on your spare superset port using those same 4 digit exts but prepended by the star digit to each, so you have *1001, *1002, *1003, etc. as key appearances on the dummy instrument.
Next in your call reroute assigment form program all of those "star" numbers to reroute always to the voice mail hunt group pilot number.
In the typical call scenario your admin answers for lawyer 'x' whose phone number is 1001. The caller asks to be placed in the lawyer's voice mail. The admin simply performs a blind transfer to *1001 and immediately releases the call. Bingo, it works.
This will work with the 3300 or SX2000 with any fully integrated voice mail system, whether embedded or 3rd party standalone (i.e., Octel)