At a bare minimum, you will need a computer, PC microphone and speakers. A step-up from speakers is to use headphones.
If you want “hands-free” conversations, you really need a headset (which incorporates a built-in microphone). And, for best quality, you may want to use a USB headset with built-in DSP (digital signal processing). Then, for the grand finale, to get maximum hands-free convenience and ultimate freedom in your home or SOHO (small office/home office), you may want to look into getting a wireless or Bluetooth headset.
At this point, I will assume you have an Internet access connection. Your Internet connection should be High-Speed Internet for best results. Now, I will say that it is possible to use a dial-up connection (56 Kbps speed) to make voice calls, but that it depends on many factors as to how successful you will be.
Now that you have your system set up, a registered softphone service installed (like Google Talk or Gmail's Video and Voice Plugin) , and your Internet connections fired-up … you’re ready to gab. Oh, it does help if you have other family members and friends who also set themselves up with PC-PC VoIP, too.
Some service providers have echo servers (like Skype's Echo123) just for the very purpose of allowing their customers to make test calls. When you call an echo server, it usually begins with a pre-recorded message and then allows you to speak, as if you were going to leave a voice message. But in the case of an echo test, the server repeats everything you say back to you. This is a very good way for you to test your system and to get reassurance that everything is working AOK. When first trying out a new VoIP system or service, an echo test is priceless. I am actually amazed that more service providers don’t have echo test servers for their clients to use. I do wish Google Talk had an echo test. If they do, I’m not aware of it.
Now that both you and your collaborating contacts both have a PC-PC VoIP system in place, just leave your softphone running on your desktop and you’re ready to make and receive PC-PC calls.... ring-ring, hello!.