[rkiechle]

i know i hate it when someone answers my question with a you should check out BLAH BLAH BLAH when you are talking about SPRINT voicemail...

But i suggest you check out google.com/voice. Their voicemail app is one of the best I have used, and I have been using it for a long time (first public beta) and now it is available for everyone for free (still)

With GROUP greetings, you should be able to accompllish exactly what you are tying to do from a browser or possibly the app.
I Don't know if they are time/date driven but I use the GROUPS messages and it allows different people that get different messages/greetings and it is very simple to change greetings.

And the ability to see/preview/delete and so on all messages from the app makes life so much easier...