Using any old PC with Linux is great way to experiment and learn about Internet Protocol (IP)-based telephony, but to implement a production server, you'll need some slightly bigger iron, and you'll need it hardened.
In my travels as a networking consultant, I get to visit a lot of enterprise data centers. These range from meager, stuffy, 100-degree closets crammed with desktop PCs that accidentally became servers, surrounded by a spaghetti pile of crummy cabling, to the 2,000-square-foot, raised-floor, uncomfortably cool server rooms with halon fire-prevention systems and row after row of racks filled with quad-processor servers.
When I have an opportunity to work in a modern, decked-out environment, I'm thankful that I'm not crammed in an undersized, overheated closet searching in vain for a free port on an incorrectly labeled Ethernet switch where I can plug in my PowerBook. It never ceases to amaze me just how little some folks seem to care about the environmental state of their critical data and communications equipment. As long as things keep running, I suppose they aren't likely to balk at the sorry state of their servers.
But with a critical application like telephony, from which humans have come to expect 100% reliability over many decades, a dilapidated hodge podge of PC equipment sitting under a leaky roof just isn't going to work. A desktop-gone-server isn't going to cut it either.
Fortunately, you're about to find out how to build ...