Skype to Skype is free, you can use Skype-out to make calls from Skype to landlines, there are no rentals but you do pay for calls.... you can find everything you need on their homepage
www.skype.com
I had a call directly from my laptop with out a headset.. there was no feedback which I have experienced in the past with Netmeeting for example. You probably would only need to buy a phone if you wanted to use Skype without a computer?
When I've used it there have been over 5 million users online!!
Jennie