This site has a ton of great hints/tips/projects utilziing the Asterisk open-source VoIP PBX project.

I found the series on using your bluetooth headset/handset as a ‘presence’ detector especially intersting.  It explains how to use this detector to route your calls automatically based on your presence or absence.  Trécool.

Nerd Vittles » 50 Great Halftime Projects Using Your Free Asterisk@Home PBX