Don't some VOIP services offer slightly less powerful versions of this? The one I used to use (Primus Canada) allowed me to set call treatments (with a limit of 50, but that was plenty for me). Some of the options included send to voicemail, forward, hang up, etc. and offered some time-of-day rules too.

It's the one big feature I miss after switching to Ooma. All I want is to direct anyone not in my contacts to voicemail by default, and add exceptions, and I can't do that. :(