ecs99ny...i don't see why that would not work.
off an auto attendant, you could do a *17 to access voicemail.
setup a USER (not HG, they don't have dtmf breakout), put option 0/2/3 (embedded is *0/*2/*3) to *20*N# (replace N with hg extension) to set the group out of service or night service.
Might setup the *2 to night/out and a *3 to clear it.
-Austin
ACE: Implement IP Office