Newer versions of Windows have come standard with an amazing array of telephony tools. An example is Microsoft's...
free, peer-to-peer program NetMeeting, which allows users to very quickly and easily establish a VoIP call and share whiteboards, screens and more. Microsoft has even dramatically improved the functionality of its Telephony API (TAPI), which allows anyone to write programs to allow their PCs and servers to be integrated with their phones. The result is lots of "Internet phones" and "soft phones" and other types of virtual devices that allow you to use Windows like a telephone.
These new features, as always, come with new risks, which you should keep in mind. The most important issue for most users is privacy. VOIP calls from such programs as NetMeeting (and just about any similar program you download off the Internet) are encoded using open standards, such as G.723 and G.729. This necessarily means that they can be DECODED with nominal effort. This is a requirement, obviously, otherwise the person on the other end of the line wouldn't be able to hear you. But unfortunately, anyone in the middle can also decode this stream. So be aware that VOIP out of the box is not encrypted and is just as easy to eavesdrop as an analog, residential phone. All that is required is access to any cable in the path, a PC, and any of a number of readily available, free software packages that sniff the traffic.
If privacy is a concern, especially if you only need it for phone calls between one or two other people, then you can also use Window's also much improved encryption features to set up an IPSec tunnel between you and the other party, and send your NetMeeting or other traffic through the tunnel. The components of this solution are all bundled with Microsoft's Windows, and are remarkably easy to configure. Be advised though, that the CPU requirements for simultaneously digitizing voice and encrypting it are substantial, so while the software won't cost you anything extra, you may want to think about a hardware upgrade.
Thomas Alexander Lancaster IV is a consultant and author with over ten years experience in the networking industry, focused on Internet infrastructure.