Suggestions for Home PBX/Key System?

foobar104 asks: "I'm fascinated by the idea of putting in a home PBX or key system. I don't really have a good justification for this; it just sounds like a neat thing to have. There are commercially available small PBX systems available for $500 to $2,000, plus another $500 to $2,000 for voicemail, but putting in one of those doesn't sound like as much fun as building one from scratch using an older PC and some off-the-shelf components. I'm wondering if anyone has suggestions for sources of information, tips, HOWTOs or other knowledge on this subject? I'm sure it's been done before; GNUCOMM and GNU Bayonne are out there, but I'm not having much luck finding tutorial-type info about them."

"The system I want to build doesn't need to be complicated. I'd like to have two outside lines and about five inside lines. I'd like the system to have all the standard cool features, like intercomm and station-to-station calls and such, but I'd also like to do some exotic things. For example, I'd like to implement a call whitelist system, where during certain hours of the day, only calls from numbers on a pre-defined "white list" ring through, and all other calls go to voicemail. I'm guessing that something like that will require programming, and I'm not afraid to get my hands dirty. I just don't know where to start.

It sounds like a fun hobby project-- to me anyway. Can anyone point me in the right direction?"