Asterisk is an open source PBX software that runs on linux. My personal opnion about it is that it's strictly for people that have too much time on their hands and work somewhere where the phones are not important or you cannot lose your job from the constant downtime. I have been to a half dozen cutomers that are linux guru nutjobs and the last time they couldn't even get one damn printer up to print the floorplans. I mean I don't like windows either but, I don't think I want to spend countless, un-profitable hours trying to implement an all linux network that runs too fricken slow to be worth a crap. Just my 2 cents.