One of the collateral benefits for business of the rise of the IP-based network we call the Internet is that you can digitise voice and use it as a telephony network - and save oodles of dosh in the process. No wonder, then, that the area of Voice over IP (VoIP) is one that is assuming ever-greater importance; indeed, it's reasonable to expect that one day VoIP will take over more or less the entire telephone system. But it's also an area shrouded in mystery, representing as it does the intersection of two very different worlds - computing and telephony.
That makes this guide to VoIP for GNU/Linux users particularly useful. It provides handy links to the main free VoIP apps, tutorials and related pages. Worth taking a look at if you want to get to grips with this area.