Basically, all you need is a headset with microphone and Skype software, and an internet connection.
There are tons of headsets out there. You can even use standard stereo headphones and the mike built into a MacBook Pro. I am using a Plantronics headset recommended by Eric Cheng which is great. $40 at Amazon.
Plantronics DSP-400 Digitally-Enhanced USB Foldable Stereo Headset and Software
You then download Skype software and follow the instructions. Easy. I signed up for the unlimited plan to call any numbers in the US and Canada for $15 per year. I can call out to anyone, any phone number, and no longer worry about long-distance charges. I believe that the rate was going to double very soon.
I did not sign up for any other stuff like the ability for people to call me, etc.
Since signing up, I've called home and other places in the US -- for free after the initial $15 annual charge -- from Singapore, England, and other places where I've had a wireless Internet connection. People think that I'm a bit strange talking into my laptop, but it works great!